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This PDF file contains the front matter associated with SPIE Proceedings Volume 11207, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.
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Fourth International Conference on Applications of Optics and Photonics
Symmetries in the propagation of a wavefield occur due to constraints, imposed either by the structure of an optical element/system or by the propagation medium. The spatial properties of a wavefield may be influenced by mirror symmetry, lateral inversion, translational and rotational symmetry. Here, we discuss various examples of light propagation under the constraints of specific symmetries. These include general aspects of light propagation, the design of micro-optical systems, rotational symmetries that occur in discretized diffractive optical elements as well as spatial and spatio-temporal properties of self-imaging wavefields.
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In this paper an optical triangulation system is used to perform the three-dimensional surface reconstruction of different textile fabrics for an objective evaluation of wrinkling. The system works by projecting a light stripe onto the surface of the fabric samples and according to the amount of wrinkling exhibited on them, the light stripe will suffer larger or smaller deviations. By moving the fabric samples relatively to the light stripe, a complete scan of the fabrics is achieved. This process leads then to the creation of 3D images of the fabrics on which it is possible to distinguish their topographic differences. With the collected data of the fabrics, it is also possible to calculate several parameters to evaluate the wrinkling quantitatively. As expected, both analyses considered in the current work are completely in agreement with the reference grades of the subjective wrinkling evaluation method.
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The performance of high-precision optical systems can be affected by the presence of mechanical stresses in the optical material. In this work, we present a ray tracing method which considers the ray’s state of polarization while propagating through a mechanically stressed lens. The framework of elastic multibody systems is used to compute stresses in optical elements and generate the information about lens deformations, refraction indices, etc. These are required for the polarization ray tracing method employed here. The proposed ray tracing scheme considers birefringence at the lens-front and uses gradient-index ray tracing within the lens. Simultaneously, the polarization states are traced with the aid of Jones vectors. Finally, the correlation of the traced polarization states and the mechanical stresses is investigated.
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Control of population inversion and coherence generation between the ground and excited states in Hydrogen–like alkali atoms is presented in this work using multiphoton π-pulse scheme with pulse durations between 100 fs to 10 ps. Density matrix (DM) equations of 4–level Rb and Cs systems are numerically solved beyond the rotating wave approximation (RWA) taking detuning and spectral chirp into account. An extension of the study is done to nP3/2 (n = 12) and nF5/2 (n = 8) of Cs atoms demonstrating the applicability of the current scheme in selective Rydberg excitation and potential extendibility to numerous configurations.
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Purpose: Accommodative anomalies are a group of different visual problems that reduce the efficiency of the visual system. Binocular accommodative facility (BAF) therapy is used to train the ability of the eye to repeatedly change its accommodative state when changing focus between two focal planes during periods of time. The aim of this study was to evaluate the effect of BAF training with standard flipper dioptric treatments on a group of non-symptomatic young adults. Material and methods: 67 subjects were recruited among students attending the Optometry Clinic of the Optometry Faculty (USC, Spain). All of them had good general health and were free of any accommodative or binocular problems. Subjects were scheduled to four session one-week apart. In each session, they were requested to measure the BAF in cycles/minute (cpm) with a ±2.00D flipper while focusing a near test at 40 cm. Patients were also requested to point the difficulty for clearing with the minus, plus or with none pair of lenses. Results: There was found a statistical difference on BAF between the first and the final session when the whole sample was analysed (paired t-test: p <0.001), and when the sample was grouped by lens clearing difficulties (paired t-test: all p ≤0.005). BAF showed a statistically significant difference between results obtained in each session (ANOVA: p =0.002), and between the results of contiguous paired sessions (paired t-test: all p ≤0.047). Conclusion: The present study showed the positive effect of traditional dioptric training in amplitude flexibility improvement.
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This work resumes the results achieved by a no-model based approach for SHM. The proposed methodology provides a signal to noise ratio improvement by cross-correlation function applied to a derived signal of the strain vector. The bonding line integrity of skin-stringer interface is the committed target, and the capability of debonding detection after low energy impact is estimated. The methodology is tested on aeronautical stiffened CFRP panels under different loading conditions after impact: residual strain, static load and quasi static load are considered. The encouraging results drove a full scale applications.
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The visual search abilities of radiologists are systematically trained due to the specifics of their professional tasks. We investigated whether the visual-motor performance of radiologists, residents and students varied when searching non-medical targets on the volumetric display. As a result, no significant differences were found in the correct response rate among three groups. However, the total number of interactions was considerably higher for the resident radiologists and medical students comparing to the experienced radiologists. Our results suggest that the radiological experience does not interfere with the outcome in the developed visual search task, but may be reflected in motor behavior.
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This paper proposes the use of nematic liquid crystals as tunable setups to implement optical analogues of physical systems and phenomena that are hard or even impossible to study experimentally under controlled conditions. Optical analogues share the same physical model with the systems that they emulate and can be understood as a form of physical simulations or optical computation. However, their success relies not only on the existence of media with optical properties capable of emulating the models associated with the original system as they interact with light, but also on the possibility of being able to tune those properties in order to cover the multitude of conditions or range of parameters. In particular, the Schr¨odinger-Newton model is a good target for this kind of studies as it can describe a plethora of different phenomena in physics and can be implemented in the laboratory using optical analogues, usually using thermo-optical materials. However, such materials have limitations, and in this work we propose nematic liquid crystals as a more advantageous alternative. We discuss how nematic liquid crystals can be used as a tunable support medium for optical analogues of superfluids by analyzing the dispersion relation of light under specific conditions and using numerical simulations based on GPGPU supercomputing to verify our findings. Extending on this, we explore more direct manifestations of superfluid effects in nematic liquid crystals, such as drag-force cancellation in the superfluid regime and the possibility of creating a roton-minimum in the dispersion relation.
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In this work we present a simulation study about the characteristics of a semiconductor structure suitable to be used as a guided wave optical biosensor, based on Surface Plasmonic Resonance effects (SPR). The proposed structure is a planar metal-dielectric waveguide where the sensor operation is based on the coupling between the fundamental propagation TM mode and the surface plasmon excited at the outer boundary of the metal, which interfaces the sample medium. Gold and aluminum are the metals considered for the plasmonic coating, amorphous silicon and others PECVD materials are considered for the waveguide structure. The results are based on modal analysis of the waveguide and plasmonic modes. The results obtained point out the possibility of generating SPPs in the near infrared range by including a functionalized cover of reduced graphene oxide (rGO) over the metal layer.
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We establish and analyze a relationship connecting the derivative of the weighted average of the phase of a surface plasmon polariton (SPP) packet with the variation of its intensity. By exploiting the angular plane-wave spectrum formalism, under the paraxial approximation, we characterize the derivatives of the weighted averages of the total phase and Guoy phase shift for Hermite-Gaussian (HG) SPP packets and analyze their dependence on the main beam parameters.
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In this paper a vehicular communication system that incorporates illumination, signaling, communications, and positioning functions is presented. The bidirectional communication between the infrastructures and the vehicles (I2V), between vehicles (V2V) and from the vehicles to the infrastructures (V2I) is performed through Visible Light Communication (VLC) using the street lamps and the traffic signaling LEDs to broadcast the information. As receivers and decoders, pin/pin SiC Wavelength Division Multiplex (WDM) photodetectors, with light filtering properties, are being used. White polychromatic-LEDs are used for lighting and to implement the WDM. This allows modulating separate data streams on four colors which together multiplex to white light. A traffic scenario is proposed, along with the transmitter to receiver setup. The performance of a cooperative driving system is evaluated. To achieve cooperative vehicular communications (I2V2V2I2V), streams of messages containing the ID physical address of the emitters are used, transmitting a codeword that is received and decoded by the receivers. As a proof of concept, a I2V2V2IV traffic scenario is presented, bidirectional communication between the infrastructures and the vehicles is established and tested. The experimental results confirm that the cooperative vehicular VLC architecture is a promising approach concerning communications between road infrastructures and cars, fulfilling data privacy.
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In this paper, a LED-assisted positioning and navigation VLC system is proposed. A VLC scenario for large environments is stablished, the emitters and receivers are characterized and the communication protocol presented. Different layouts are analyzed. Square and hexagonal meshes are tested and a 2D localization design, demonstrated by a prototype implementation, is presented. The key differences between both topologies are discussed. For both, the transmitted information, indoor position, motion direction as well as bi-directional communication are determined. The results showed that the LED-aided VLC navigation system make possible to determine the position of a mobile target inside the network, to infer the travel direction along the time and to interact with information received.
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Quantitative phase imaging is widely used in biomedical and industrial applications for morphology and dynamics characterization of various unstained samples with nanoscale sensitivity. Registration of phase images in multiple narrow wavelength bands enables analysis of spectral properties as well as extending the dynamic range and increasing the accuracy of quantitative phase measurements. In this paper, we present a new scheme for hyperspectral quantitative phase imaging, based on acousto-optic filtration of light in lens-in-lens common-path interferometer. It may be implemented as a PC-controlled compact add-on module for light microscope, has a robust and vibration insensitive design, and allows a quantitative phase imaging of various samples. Acousto-optic filtration provides fast and arbitrary wavelength tuning within a wide range with high spectral resolution. Choosing proper parameters of the interferometer and acousto-optical filter allows adapting the proposed scheme to many microscopy applications.
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Atmospheric aerosol particles were collected at Camag¨uey (21.42° N, 77.85°W, 122 m asl), Cuba, during 2010 and 2012-2014, for investigating the absorption of light by particles, particulate matter (PM) concentration, and elemental composition. Samples were collected with a low volume particulate Dekati PM10 impactor twice a week with a collection time of 24 hours. The sample flow rate was 15 l/min. Gravimetric analysis of the particulate matter fractions PM1 (PM< 1 μm) was carried out for 104 samples. An Integrating Sphere Spectral System (IS3) was developed for measuring the spectral absorption coefficient from the UV to the visible wavelengths with a spectral resolution of 10 nm. The system uses a filter-based method. The light absorption is determined by measuring and comparing the intensity of light transmitted by filters with and without particles deposited. The IS3 is fully described in this work. It consists of a 6-inch integrating sphere with a spectral reflectance of 98 % that covers the wavelength range from 250 to 2500 nm. The light source includes a 150W xenon lamp included in an ORIEL APEX illuminator equipped with a transmission filter, and an automated scanning monochromator. The signal is detected by a compact size Si detector (200-1100 nm) connected to a light meter. With this approach continuous spectra of the absorption coefficients in the 320-800 nm spectral range can be obtained with variable spectral resolution. Spectral absorption coefficients measured by the IS3 are presented and analyzed for the campaign period.
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In this paper we describe a compact optoelectronic circuit for spike-free nanosecond pulse generation in semiconductor lasers. The device is designed to work as an injection seeder in high-power fiber lasers built in master oscillator power amplifier architecture. To reduce a significant pulse distortion resulted from relaxation oscillations, a technique called light injection was used. It allows achieving the pulse generation with excellent temporal and spectral properties. Smooth pulses with duration of 1.9ns and narrowband spectrum with a central wavelength of 1550nm have been presented experimentally.
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Indoor navigation based on Visible Light communication (VLC) are attractive solutions for Indoor Positioning Systems, as Global Positioning Systems signals are strongly absorbed by the buildings and other wireless solutions need to be used. In this work it is proposed an indoor navigation system based on VLC technology for assisting warehouse management with autonomous vehicles. The system is designed to establish bidirectional communication between a static infrastructure and the mobile picking robot. Data transmission uses white tri-chromatic LEDs as optical emitters, a dedicated photodetector with selective spectral sensitivity and different coding schemes designed to ensure synchronization between frames, to shield the decoding process from errors and to minimize flickering effects.
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In this work, we present a parametrical characterization of the features of the total electric field induced in a material in response to an external incident field. We propose global parameters enabling characterization of the volume in which the squared modulus of the induced electric field is mainly concentrated, as well as the predominant state of polarization over the region where the power is significant. In addition, an uncertainty relationship is presented linking the region of concentration of the induced electric field and the region where its maximum rate of change occurs.
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In this paper we present a simulation study that intends to characterize the influence of defects introduced by manufacturing processes on the geometry of a semiconductor structure suitable to be used as a multimode interference (MMI) 3 dB power splitter. Consequently, these defects will represent refractive index fluctuations which, on their turn, will drastically affect the propagation conditions within the structure. Our simulations were conducted on a software platform that implements both Beam Propagation and FDTD numerical methods. This work supports the development of a biomedical plasmonic sensor, which is based on the coupling between the propagating modes in a dielectric waveguide and the surface plasmon mode that is generated on an overlaid metallic thin film, and where the output readout is achieved through an a-Si:H photodiode. By using a multimode interference 1×2 power splitter, this sensor device can utilize the non-sensing arm as a reference one, greatly facilitating its calibration and enhanced performance. Amorphous silicon can be deposited by PECVD processes at temperatures lower than 300°C, an attractive characteristic which makes it back-end compatible to CMOS fabrication processes. As the spectral sensitivity of amorphous silicon is restricted to the visible range, this sensing device should be operating on a wavelength not higher than 700 nm, thus a- SiNx has been the material hereby proposed for both waveguides and MMI power splitter.
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White-light interferometry is an established and proven method for precise measurement of the shape of objects. Shape of objects with both smooth and rough surface can be measured. However, white-light interferometry suffers from some limitations. One of them is that the measured object must be mechanically moved relative to the measuring device during the measurement. We present an optical 3D sensor based on white-light interferometry that can measure the shape of objects without the mechanical movement of the object. Instead of the object, the reference plane moves and scans the shape of the object. A part of the imaging system is an electrically tunable lens that ensures that the measured part of the object is sharply imaged during the whole measuring procedure. The movement of the reference plane is done by the movement of reference mirror or by use of fiber optic modulation interferometer.
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In this work we will present a new diode-pumped, OPCPA-based few-cycle, high energy, high power mid-infrared laser system, providing few-cycle pulses at high repetition rate. Plans for its subsequent amplification to the mJ level at 10 Hz are also shown.
These lasers will be used as the main drivers for high harmonic generation and laser-plasma acceleration experiments in Portugal. Additionally, they will be open for access by external users. This will be an unprecedented experimental capability at the national level, allowing experiments in a novel physical regime.
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Gold nanoparticle-mediated hyperthermia is a non-invasive, target-based cancer treatment with significantly reduced side effects compared to conventional treatments. In this work a simulation model for gold nanoparticlemediated hyperthermia is set up and used to investigate the case of a liver tumor located in the vicinity of a hepatic vein. Gold nanorods with optimized size and aspect ratio are embedded within the liver, and the temperature raise under CW laser illumination is calculated, while taking into account the convective heat transfer through blood perfusion. For this purpose, an analytical model based on the Navier-Stokes equation is used. Results show that due to the heat drain in the blood stream, an effective temperature raise is not achievable when the tumor is located in the vicinity of the hepatic vein. Additionally it is shown that even in the case of a 90% occluded vein, the temperature raise with such nanoparticle arrangement is still not enough for tumor ablation.
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In this work, we perform a numerical investigation on the performance of different nonlinear optical media for ultrabroadband OPCPA at 3 μm operating wavelength, when pumped by a high energy source at 1030 nm. We compare the energy and bandwidth gain, as well as the conversion efficiency achieved through a set of available high-damage nonlinear crystals transparent at these wavelengths. Specifically, we demonstrate the potential for scaling the mid-IR OPCPA output to the multi-mJ-level. We discuss the main challenges for the implementation of a new ultrafast, high energy mid-IR source at the L2I facility and the potential applications of such a system.
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Over the past 20 years, research into Gallium Nitride (GaN) has evolved from LED lighting to Laser Diodes (LDs), with applications ranging from quantum to medical and into communications. Previously, off-the-shelf GaN LDs have been reported with a view on free space and underwater communications. However, there are applications where the ability to select a single emitted wavelength is highly desirable, namely in atomic clocks or in filtered free-space communications systems. To accomplish this, Distributed Feedback (DFB) geometries are utilised. Due to the complexity of overgrowth steps for buried gratings in III-Nitride material systems, GaN DFBs have a grating etched into the sidewall to ensure single mode operation, with wavelengths ranging from 405nm to 435nm achieved. The main motivation in developing these devices is for the cooling of strontium ions (Sr+ ) in atomic clock applications, but their feasibility for optical communications have also been investigated. Data transmission rates exceeding 1 Gbit/s have been observed in unfiltered systems, and work is currently ongoing to examine their viability for filtered communications. Ultimately, transmission through Wavelength Division Multiplexing (WDM) or Orthogonal Frequency Division Multiplexing (OFDM) is desired, to ensure that data is communicated more coherently and efficiently. We present results on the characterisation of GaN DFBs, and demonstrate their capability for use in filtered optical communications systems.
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In ground based astronomical observations, atmospheric dispersion shifts the image of the object at different wavelengths due to the wavelength-dependent index of refraction of the atmosphere. Thus, using an Atmospheric Dispersion Corrector (ADC) is mandatory in order to avoid any wavelength dependent losses. Typical ADC configurations, for high resolution astronomical instruments, are two counter-rotating prisms, a set of, at least, four prisms paired together. With the arrival of large telescopes with higher angular magnification, and spectrographs with higher resolution, the requirements on the dispersion correction are becoming more critical due to the impact on the produced science (e.g. radial velocity precision). We developed an ADC optical design tool in order to select the best set of glasses in terms of residuals, transmission, resulting image quality, Fresnel losses, taking into account the required spectral range and typical atmospheric conditions where the ADC will be working. A demonstration of the capabilities of the tool is presented with the analysis of the impact of different melt data, the effect of different glass Sellmeier coefficients between catalog and measured ones, that can create a difference in the residuals above few tens of milli-arcseconds (mas). The tool allows the investigation of critical steps on the ADC design phase and speeds up the glass selection process critical for the harder requirements of the future instruments/telescopes.
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In this work, the paraxial evolution of fields generated by pseudo-Schell vortex sources is analyzed through some global parameters. In particular, it is shown that the kurtosis parameter of these fields presents a minimum at the beam waist and a maximum which value and position depends on the coherence characteristics of the source.
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The aberrations demonstrate the changes in light direction when it passes through the eye’s optical system. Our study goal was to evaluate the impact of keratoconus apex’s localization on eye aberration. 79 eyes were analysed in our study by keratoconus stage and by apex localization. Vertical coma had a statistically significant difference p=0.03 (Mann-Whitney test) between first (1.4 μm) and third (3.9 μm) keratoconus stage. The mean spherical aberration in case of central apex was 0.6 μm and in case of peripheral apex was 1.0 μm (p=0.01). The keratoconic eyes have increased corneal aberrations comparing to normal eyes.
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The combination of magnetic nanoparticles and hydrogels affords magnetogels, improving the manipulation of physicochemical properties and widening the range of applications, such as magnetic resonance imaging, biosensing, hyperthermia, drug delivery and as a template material. The introduction of plasmonic properties will synergistically enhance anticancer therapeutic strategies on the desired target through photothermia, drug release and photodynamic therapy. In this work, superparamagnetic manganese ferrite (MnFe2O4) nanoparticles coated with a gold shell were successfully incorporated into a self-assembled peptide-based hydrogel linked to a naproxen group, a lysine residue to stabilize the gold nanoparticle surface, and a dehydroamino acid that provides protease resistance. The new magnetogel was evaluated as nanocarrier for the model drug curcumin and the photothermia potential of the nanosystem was assessed. Microstructural properties of the hydrogels and magnetogels were studied by CD. Fluorescence-based techniques (fluorescence emission, quenching and FRET) were used to assess hydrogel physicochemical properties, incorporation of drugs and drug transport towards model membranes. The developed magnetic/plasmonic nanosystem exhibited promising results for photothermia application in multimodal cancer therapy, though future combination with other hydrogels will be required to improve its applicability.
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Being motivated by the recent result on the emergence of superlattice properties of the helical nanoribbon in an electric field, we analyze its circular dichroism signal. We theoretically demonstrate that electric-field effect on the helical nanoribbon leads to appearance of new spectral lines in circular dichroism.
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Observations with ground-based telescopes are affected by differential atmospheric dispersion when seen at a zenith angle different from zero, a consequence of the wavelength-dependent index of refraction of the atmosphere. One of the pioneering technology in detecting exoplanets is the technique of radial velocity (RV), that can be affected by uncorrected atmospheric dispersion. The current highest precision spectrographs are expected to deliver a precision of 10 cm s−1 (e.g., ESPRESSO). To minimize the atmospheric dispersion effect, an Atmospheric Dispersion Corrector (ADC) can be employed. ADC designs are based on sky dispersion models that nonetheless give different results; these can reach a few tens of milli-arcseconds (mas) in the sky (a difference up to 40 mas); a value close to the current requirements (20 mas in the case of ESPRESSO). In this paper we describe tests done with ESPRESSO and HARPS to understand the influence of atmospheric dispersion and its correction on RV precision. We also present a comparison of different sky models, using EFOSC2 data (between 600nm and 700nm), that will be used to improve on the design of ADCs.
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ESPRESSO is a fibre-fed, cross-dispersed, high-resolution, echelle spectrograph developed to fully exploit the European Southern Observatory VLT (Very Large Telescope), and it was open to the astronomical community at the end of 2018. This spectrograph was installed at the Combined Coudé Laboratory (CCL) of the VLT, fed by four Coudé Trains, which bring the light to the CCL from the Nasmyth platforms of the four 8.2-metre Unit Telescopes. With all four Telescopes combining their light-collecting power to feed a single instrument, the ESPRESSO Coudé Train effectively transforms the VLT into the largest optical telescope in the world in terms of collecting area. The Coudé Train is composed of a set of prisms and lenses delivering a pupil and an image to the CCL, up to 70 m away, including an Atmospheric Dispersion Compensator. The use of only refractive optics, namely Total Internal Reflection prisms, has the advantage of the inherent higher throughput, especially in the blue region of the spectrum. With these complex optics, ESPRESSO can either collect the light from up to all four Unit Telescopes together, or alternatively receive light from any one of the telescopes independently, allowing for more flexible usage of observing time. In this paper, we present the ESPRESSO Coudé Train concept, the design and the implementation on the VLT.
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A femtosecond laser direct writing system was developed to explore the fabrication of periodic structures in optical fibers. The possibility to write type I first- and second-order Bragg gratings in the same single-mode fiber (SMF-28e), with reflectivities of 99.6 % and 59.3 %, respectively, is presented. The fabrication of structures (waveguides and grating) in a coreless and in a SMF-28e fiber was first demonstrated, and the gratings were then exposed to a thermal annealing up to 1000°C. The FBG inscribed in the SMF-28e fiber presents thermal stability at temperatures of 800 °C and a temperature sensitivity of 14.34 pm/°C was determined.
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Hollow microsphere fiber sensors are Fabry-Perot interferometers (FPI) that can be used for lateral loading, temperature, and refractive index sensing. In this work, graphene oxide (GO) is explored as a tunable platform for enhancing the spectral properties of hollow microsphere fiber sensors. GO offers similar mechanical and optical properties as graphene, with the advantage of a wider range of deposition methods and a lower cost. The influence of multilayer coatings of polyethylenimine (PEI) and GO, achieved with the layer-by-layer technique, on the reflectivity of the outer surface, and hence, on the spectrum of the FPI for maximum of 30 bilayers was studied. The obtained results revealed a change of the microsphere outer surface reflectivity and also of visibility of the reflected spectrum when varying the number of bilayers. A maximum signal amplitude of 3.9 dB was attained for the 13th bilayer, allowing to conclude that PEI/GO multilayer coatings can be used for enhancing desired properties of the three-wave FPI for different sensing applications.
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Both in medicine and optometry, clinical guidelines have become a relevant part of clinical practice decision making process. In our study, we aimed to refer to potential limitations related to specific undefined guidelines used in optometry that suggest near addition (add) values based on patient age. We measured near add binocularly at 40 cm distance with plus build up technique in 216 adults aged 35 to 80 years. Baseline subjective refraction, near visual acuity with and without add was analysed in a relation to age and the amount of near add. For further analysis, we randomly selected 30 patients and performed five different near add estimation techniques. Our results support that there is a positive, linear relationship of moderate strength between age and amount of near add (r = 0.73, P < 0.05). Relationship is positive and fairly strong (r = -0.78, P < 0.05) between near visual acuity without add and near add amount and moderate (r = -0.51, P < 0.05) between near visual acuity without add and patient age. Differences between plus build up technique is not statistically significant if compared with other clinical near add estimation techniques (P > 0.05). Guideline based technique (P < 0.01) provided 0.29 D higher near add while technique based on calculations from amplitude of accommodation (P < 0.01) provided 0.65 D lower near add. Based on our results, we highlight that usability of age expected near add in clinical environment is limited because of large individual differences.
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One of the most common image denoising technique used in Optical Coherence Tomography (OCT) is the frame averaging method. Inherent to this method is that the more images are used, the better the resulting image. This approach comes, however, at the price of increased acquisition time and introduced sensitivity to motion artifacts. To overcome these limitations, we proposed an artificial neural network architecture able to imitate an averaging method using only a single image frame. The reconstructed image has an improvement in the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) parameters compared to the original image. Additionally, we also observed an improvement in the sharpness of the denoised images. This result shows the possibility to use this method as a pre-processing step for real-time tissue classification in smart laser surgery especially in bone surgery.
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This paper reports the development of a numerical module for the HiLight simulation platform dedicated to the propagation of light in nonlocal nonlinear optical media and the adaptions implemented for it to be used as a numerical test-bed to evaluate the impact of new extensions of the Theory of General Relativity in the dynamics of a N-body system. The phenomenology of light in nonlocal and nonlinear media is very rich and can be described by a multitude of effective models, with different levels of detail and approximations, which coincide with few or no differences with those found in many other fields of physics. In particular, nonlocal extensions of the Generalized Nonlinear Schr¨odinger equation (also known as the generalized Schr¨odinger-Newton system) constitute a wide class of physical models that can be found in both optics and in the studies of alternative theories for gravity. Therefore, numerical solvers developed for the former can be adapted to address the later. Indeed, this paper discusses the adaptation of a numerical solver of the generalized Schr¨odinger-Newton system based on GPGPU supercomputing, initially developed to investigate the properties of light in exotic nonlocal media, to tackle the dynamics of large distributions of matter whose interaction is governed by extensions of the Theory of General Relativity, namely those based on non-minimal coupling between curvature and matter. This paper analysis the structure of the resulting simulation module, its performance and validation tests.
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This paper explores and compares three different plasmonic optical fibre sensor configurations, based on D-type and suspended core fibres combined with metallic nanowires, and investigates how their different geometrical parameters can affect the coupling between the guided optical mode supported by fibres and the localized plasmonic modes, and how that ultimately results in improved sensor performance. Fibre optical sensors based on plasmonic resonances with metallic nanostructures have revolutionized the field of optical sensing because they have permitted to obtain sharper and fine-tuned resonances with higher sensitivity. The essence for exploring the properties of localized plasmonic modes and their coupling with the optical guided mode depends not only on the choice of the materials employed in the device, but also on the geometry of the different components and their relative position, which ultimately determines the spatial distributions of optical power of the different modes and consequently their overlap and coupling. In this work, we use numerical simulations based on finite element methods to demonstrate the importance of shaping the features of the guided optical mode to promote the coupling with the localized modes, in the two types of fibres considered. The results clarify some of the fundamental aspects behind the operation of these devices and provide novel proposals for enhanced refractive index sensors.
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A Fabry-Pérot interferometer was fabricated inside a fused silica substrate through femtosecond laser micromachining. The influence of the waveguide’s writing parameters on the measured signal’s quality was studied for an interferometer with a 27-μm wide cavity. Optimal signal-to-noise ratio and fringe visibility were obtained for waveguides written at 75 nJ and 50 μm/s. The same device was characterized with different refractive index liquids, and a maximum sensitivity of 1181.4±23.6 nm/RIU was obtained in the index range of 1.2962 to 1.3828 (at 1550 nm) for the spectral order 𝑚 = 46.
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We report on the development of numerical module for the HiLight simulation platform based on GPGPU supercomputing to solve a system of coupled fields governed by the Generalized Nonlinear Schr¨odinger Equation with local and/or nonlocal nonlinearities. This models plays an important role in describing a plethora of different phenomena in various areas of physics. In optics, this model was initially used to describe the propagation of light through local and/or nonlocal systems under the paraxial approximation, but more recently it has been extensively used as a support model to develop optical analogues. However, establishing the relation between the original system and the analogue, as well as, between their model and the actual experimental setup is not an easy task. First and foremost because in most cases the governing equations are nonintegrable, preventing from obtaining analytical solutions and hindering the optimization of the experiments. Alternatively, despite numerical methods not providing exact solutions, they allow to test different experimental scenarios and provide a better insight to what to expect in an actual experiment, while giving access to all the variables of the optical system being simulated. However, the numerical solution of a system of N-coupled Schr¨odinger fields in systems with two or three spatial dimensions requires massive computation resources, and must employ advanced supercomputing and parallelization techniques, such as GPGPU. This paper focuses on the numerical aspects behind this challenge, describing the structure of our simulation module, its performance and the tests performed.
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Our aim was to analyze viewing distance for smartphone users (aged 18-45 y.) in terms of passive or active task, relation to heterophoria, type of refractive error and smartphone font size. Participants were asked to read out loud text message (passive task) and afterwards rewrite the same text and send back (active task). For the text message we used sentence consisting of 23 words and 200 characters (with spaces). Participants used their own smartphones (font size monitored). For both passive and active task we measured task time and viewing distance at the end of the task. We found significantly shorter viewing distance for digital active task compared to passive task (29.3 ± 4.7 and 32.3 ± 6.0 cm) and also for digital passive task compared to hardcopy passive task (32.3 ± 6.0 and 34.4 ± 5.9 cm). There was no difference between viewing distance with and without low plus lenses (low add) for digital active task (29.9 ± 5.4 and 29.3 ± 4.7 cm) and for digital passive task (31.4 ± 6.4 and 32.3 ± 6.0 cm). Viewing distance and reading/writing speed was not influenced by type of refractive error and heterophoria type. The interaction between task type and heterophoria type was not significantly associated neither with viewing distance (P = 0.77), nor relative viewing distance (P = 0.54). Writing speed decreased significantly with age (P < 0.001), while reading speed was not influenced by the age (P > 0.05). The explanation, why some people prefer closer viewing distance when using smartphone, seems to be more related to task type and relatively shorter length of forearm not type of refractive error or near heterophoria type.
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The mechanical properties of bio-engineered tissues have to be determined to evaluate their quality and clinical viability. Even today, the methodology applied to analyze any biomaterials requires their destruction, involving minimum conditions of repeatability. Thus, a new integrated experimental device has been developed based on the Laser Speckle Rheology technology, which is a method of non-contact optical approach, based on dynamic light scattering. This method enables to characterize a sample without modify and destroy it, allowing a subsequent clinical use.
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In this study we use the Functional Vision Screening Questionnaire (FVSQ) to identify functional indicators of visual problems among a sample of older people living in nursing homes. An important proportion of residents under study have difficulties on the performance of distance and near vision tasks. We have found a high proportion of blanks in several items of the FVSQ that seems to suggest the need to adapt the functional indicators of FVSQ to the vision-dependent daily activities of our residents.
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As quantum-driven processes and properties start to shape the future of technology, quantum simulations appear as a crucial piece of the puzzle, acting both as building blocks and catalysts for the improvement of the understanding of unique quantum features. In essence, they can be understood as a class of prototype experiments that allow a study of quantum properties in a controllable environment. In this context, quantum fluids of light are one of the strongest candidates for this role as coherent behavior is easily accessible and not hidden by detrimental thermal noise usually present in more common quantum systems. In this work we explore the underlying theory of quantum fluids of light in propagating geometries through the hydrodynamic interpretation of light, where photons behave as interacting particles in the presence of a nonlinear medium. Exploiting the highly controllable optical properties of atomic systems and their enhanced nonlinear properties related to quantum coherence phenomena, we discuss how they can be used to set a tunable platform for quantum simulations. As examples, we demonstrate a series of quantum features of this light fluid in the form of super fluidic-like behaviors, ranging from the more common and experimentally confirmed suppressed scattering, drag-force cancellation and Bogoliubov-like dispersion relation for the elementary excitations, to other interesting phenomena yet to be explored, such as the case of persistent currents.
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The interaction of light with matter in near-to-resonant conditions opens a path for the exploration of nontrivial optical response that can play an important role in future photonics-driven technology. But as the attention shifts towards many-level atomic systems and involving multi-dimensional experimental scenarios, the complexity of the physical systems makes the analytical approach to the semiclassical model of the Maxwell- Bloch equations impossible without any strongly-limiting approximations. In this context, robust and high-performance computational tools are mandatory. In this work, we describe the development and implementation of a cross-platform Maxwell-Bloch numerical solver that is capable to exploit the different hardware available to tackle efficiently the problems under consideration. Moreover, it is demonstrated that this simulation tool can address a vast class of problems with considerable reduction of simulation time, featuring speedups up to 30 when running in massive parallel GPUs compared with the same codes running on a CPU, showing its potential towards addressing a large class of modern problems in photonics.
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Solitons are localized wave solutions that appear in nonlinear systems when self-focusing effects balance the usual pulse dispersion of common optical media. Their stability and particle-like behavior make them ideal candidates for applications that range from communication to optical computing, but in real world physical systems, dissipative processes makes these otherwise stable solutions unstable, and true solitons are particularly hard to observe in systems featuring non-negligible dissipation. In these cases a special type of localized stable solutions, called dissipative solitons, are still possible to obtain, if in addition to a balance between diffraction and nonlinearity, an equilibrium between gain and loss is also present. In this work we discuss theoretically how a 4-level atomic system and an incoherent pumping process can be an ideal experimental testbed for studying this interesting class of solutions, featuring tunable optical properties and controllable gain/loss dynamics that allow to study both classes of temporal and spatial dissipative optical solitons.
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Purpose: Tear film meniscus evaluation offers a non-invasive indication of the total volume of the tear. The aim of this study was to analyse the relationship between the central tear meniscus area with symptomatology and tear film stability. Material and methods: 120 participants who completed an OSDI questionnaire were enrolled in the study. After fluorescein instillation, two videos were recorded by a digital camera attached to a slit-lamp. The first video recorded the lower central portion of the tear meniscus (6 o’clock) with a short light beam (3x5mm), and the second one recorded the complete ocular surface obtaining the Break-Up time (BUT) and Maximum Blink Interval (MBI). A self-design program (FWCapture) was used to acquire the videos while the participants were requested to keep the eye open for as long as possible three times. Images were extracted from each video by a masked observer. From de first video, Central Tear Meniscus Area with fluorescein (CTMAF) was “manually” measured by using ImageJ software (command “<<freehand tool”). From the second video, BUT and MBI were determined by counting video frames then converted in seconds; both parameters were averaging using only the two most similar measurements. Results: CTMAF showed a negative correlation with OSDI score (Spearman Rho: p <0.001, r=-0.372). There was found a statistical difference in the CTMAF between OSDI subgroups (Kruskal-Wallis: p=0.001). CTMAF showed a positive correlation with BUT/MBI (Spearman Rho: both p ≤0.003, r≥0.246). Conclusions: Tear film volume showed a relationship with the symptomatology and tear film stability.
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Purpose: Meibography images bring information about the status and integrity of the meibomian glands (MG). The aim of this study was to correlate the meibomian gland loss area (MGLA) with age and dry eye symptomatology. Material and methods: A total of 110 subjects were recruited for the study. From the Meibography images obtained with the Topcon® CA-800 topographer, MGLA was calculated as the difference between the total area of the tarsus and the MG presence area measured by using the ImageJ software. Before examination, all subjects completed an OSDI questionnaire. OSDI scores were grouped in 4 severity categories: normal (score ≤12), mild (score 12–22), moderate (score 22–32) and severe (score ≥32). Age were categorised in 3 subgroups: ≤25 years, from 25 to 45 years and ≥45 years. MGLA was also grouped in 4 categories of loss: ≤25 %, from 25 to 50%, from 50 to 75% and ≥75%. Results: Analysis was performed by dividing the sample in the 4 MGLA subgroups; these subgroups showed differences in age (p=0.029; Kruskal-Wallis test) and differences in OSDI scores (p=0.001; Kruskal-Wallis test). Sample was divided in 3 age subgroups and differences were obtained in MGLA values among subgroups (p<0.001; Kruskal-Wallis test). Samples was divided in 4 OSDI subgroups and differences were obtained in MGLA values among subgroups (p=0.003; Kruskal-Wallis test). Positive correlation (Spearman Correlation) were obtained for both, MGLA vs. age (r=0.329, p<0.001) and MGLA vs. OSDI (r=0.380, p<0.001). Conclusion: In the present study MGLA showed a relationship with age and OSDI.
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Purpose: Tranaglyphs and Vectograms are visual therapy material based on red/green or polarized targets respectively that used similar but slightly different images for each eye to train fusion and vergence skills. This study aimed to analyse the relationship of three accommodative parameters (the Negative Relative Accommodation [NRA], the Positive Relative Accommodation [PRA] and the Accommodative Amplitude [AA]) with the results of four different visual therapy vectograms/tranaglyphs. Material and methods: 45 subjects free of any accommodative or binocular problem were recruited among students attending the Optometry Clinic of the Optometry Faculty (USC). In a first session, the accommodative tests were performed according to their standard protocols. In a second session, following manufacturer’s instructions, the subjects performed in a random order four different calibrated vectograms/tranaglyphs: two red/green Variable Demand Anaglyphs (one based on circles [VDA-C] and one on draws [VDA-D]), one red/green Fixed Demand Anaglyph [FDA], and one polarized with Variable Demand [VDP]. Subjects were asked to indicate the maximum value both base-out (BO) and base-in (BI), where the image fusion was lost. Results: NRA showed a negative correlation with the BO results of the VDP (p = 0.040, r = -0.270). PRA showed a negative correlation with the BO results of the VDA-C, the VDA-D and the VDP (all p ≤0.017, r ≥ -0.323). AA showed a positive correlation with the BI results of the VDA-D, the FDA, and the VDP (all p ≤0.013, r ≥0.341). Conclusion: Accommodation seems to have some influence on the visual therapy training with vectograms and tranaglyphs.
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Purpose: Vital staining is one of the most widely test used to evaluate the corneal damage. The aim of this study was to assess the relationship of the corneal damage with tear meniscus height (TMH) and dry eye symptomatology. Material and methods: 530 subjects were recruited among patients of the Optometry Clinic (USC). Previously, all of them completed an OSDI questionnaire. Two videos of the ocular surface were recorded from each patient by a digital camera attached to a slit-lamp. Firstly, a video of central tear meniscus under 40x with the Tearscope device illumination was recorded. From those videos, a masked observer extracted one image and TMH was measured by using the ImageJ software. Secondly, after fluorescein instillation, the corneal surface was recorded by another experienced masked observer, who assigned a category to the corneal damaged based on the Oxford Scheme. The evaluation was stratified by corneal zones based on the CCLRU grading scales (central, superior, inferior, nasal and temporal). Results: When the sample was grouped by the corneal staining Oxford Grade, there was found a statistical difference between groups in OSDI and TMH value (ANOVA: both p≤0.006). There was found a difference in OSDI value when corneal damage was in nasal or inferior areas (t-test; both p≤0.015), and a difference in TMH value arises when damage was in the central, nasal or inferior areas (t-test; all p≤0.013). Conclusions: There is a relationship between corneal damage grade and corneal zones with dry eye symptomatology and tear film volume.
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Ana Belén Rodríguez-Águila, Alejandro Toral-López, Juan de la Cruz Cardona, Ana M. Ionescu, Noel Rodríguez, Francisco G. Ruiz, Andrés Godoy, Maria del Mar Pérez
Proceedings Volume Fourth International Conference on Applications of Optics and Photonics, 112071E (2019) https://doi.org/10.1117/12.2527355
The optical properties of transparent conductive electrodes (TCEs) based on indium tin oxide (ITO) films deposited on polyethylene terephthalate (PET) substrates were evaluated in this work making use of the Inverse Adding-Doubling (IAD) iterative method. This technique allowed us to obtain the scattering and absorption coefficients explaining the optical behavior of the ITO-PET samples. The results pointed out that absorption is the most noticeable optical extinction process that occurs when light travels through this material.
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Purpose: Primary angle-closure glaucoma is a common cause of blindness where angle closure is a fundamental pathologic process. Van Herick technique is one of the commonest tests used in clinical settings for iridocorneal angle estimation, but training is required. With the development of imaging devices for the anterior segment of the eye, such as multi-diagnostic platform VX120 (Visionix), objective quantification of the angle can be obtained. The purpose of this study is to compare the angle estimation of Van Herick (with the aid of image processing software) with that obtained by objective VX120 platform. Material and methods: 49 subjects were enrolled in the study among patients attending the Optometry Clinic of the Optometry Faculty (USC). All of them were assessed with multi-diagnostic platform VX120 (Visionix) in order to obtain the Anterior Chamber Depth (ACD) and temporal iridocorneal angle (TA) parameters. Then, an image of the temporal optic section of the cornea (following the requirements of Van Herick technique) was obtained from each subject by using a camera attached to a slit-lamp. Finally, Van Herick’s temporal angle was determined as a ratio between the peripheral anterior chamber depth and corneal thickness (AC/SC ratio) by using ImageJ software. Results: Van Herick´s AC/SC ratio showed a significant correlation with both TA (r=0.389, p=0.006) and ACD (r=0.370, p=0.009). As expected, both VX120 parameters (ACD and TA) showed a significant correlation between them (r=0.863, p<0.001). Conclusions: Van Herick´s AC/SC by using ImageJ software supposes a valuable parameter for iridocorneal angle estimation.
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In the present communication, we describe how to produce long light distributions in the focal area of a high numerical aperture optical system using a custom modulation function with spiral charge. This analysis expands our previous developments in the field. We analyze the effect of this new element on the behavior of light along the optical axis.
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We recently reported that phase encoded samples produced with metallic components (e.g. gold nano-particles) can be distinguished by means of polarized light. Classification was carried out using data obtained from speckle distributions. Despite this approach is very successful, it cannot be used with codes made of materials that do not change the state of polarization of the illumination source. In the present communication we analyze the feasibility of using optical diffusers as polarizing phase encoders for optical security systems. Preliminary optical results seem to support our thesis.
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Sensing at small dimensions in biological and medical environments requires miniaturized sensors with high sensitivity and measurement resolution. In this work a small optical fiber probe was developed to apply the Vernier effect, allowing for enhanced temperature sensing. Such effect is an effective way of magnifying the sensitivity of a sensor or measurement system in order to reach higher resolutions. The device is a multimode silica Fabry-Perot interferometer structured at the edge of a tapered multimode fiber by focused ion beam milling. The Vernier effect is generated from the interference between different modes in the Fabry-Perot interferometer. The sensor was characterized in temperature, achieving a sensitivity of -654 pm/°C in a temperature range from 30°C to 120°C. The Vernier effect provided a temperature sensitivity over 60-fold higher than the sensitivity of a normal silica Fabry-Perot interferometer without the effect. The temperature resolution obtained was 0.14°C, however this value was limited by the resolution of the OSA and can be improved further to less than 0.015°C.
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The fabrication of optical waveguides with femtosecond laser direct writing is reported in two materials, Suprasil1 and Eagle2000. The influence of typical fabrication parameters, such as pulse energy and scan velocity, on the waveguide’s spectral characteristics is explored from 500 to 1700 nm. Tests conducted in Suprasil1 evidence a strong presence of Rayleigh scattering, hindering the production of low-loss waveguides at short wavelengths. On the other hand, optical waveguides fabricated in Eagle2000 exhibited lower insertion losses at short wavelengths, enabling the fabrication of low-loss broadband optical waveguides with a two order of magnitude higher scan velocity when compared with Suprasil1.
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Scattering-type Scanning Near Field Optical Microscopy (s-SNOM) has been demonstrated as a valuable tool for revealing important properties of materials at nanoscale. Recent proof-of-concept experiments have shown that, among others, s-SNOM can provide quantitative information on the real and imaginary parts of the dielectric function, and hence of intrinsic optical properties of materials and biological samples. In this work we further explored these capabilities in several experiments dealing with microcapsules for drug delivery, ultra-thin optical coatings with tunable color properties, and two types of nanoparticles with important applications in energy storage and conversion, or biosensing and theranostics.
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The lighting systems that is used in our daily tasks are an important factor in our vision quality. These systems must be suitable to the visual needs required by these type of tasks. The aim of this work is to evaluate the influence of coloured lighting on ocular accommodation and quantify its response with the lighting used. Twenty subjects, with ages ranged from 18 to 26 years old, participated in the study. All subjects had 20/20 corrected visual acuity or better, normal colour vision and no history of ocular disease or surgery. The amplitude of accommodation was measured and compared under normal lighting conditions (assuming white LED light) and under coloured LED lighting tuned at peak wavelengths of 515 nm and 635 nm. Improvements over the reference light source on the parameters that were analysed will be identified and assumed as better lighting conditions (>0.05). It was found a general decrease on the amplitude of accommodation when measured under coloured lighting and compared against the normal lighting. The most statistically significant decrease was found for the red light with a difference of 1.45D (p=0,05). Special care was taken to ensure same viewing and illuminance on all test conditions. These results seem to suggest that there is an impact of the colour of the lighting in use in the availability of the amplitude of accommodation.
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This study aimed to investigate if the compensation effect that exists between cornea and the internal optics of the eye changes with a computer near vision task. Nineteen emmetropic students of University of Minho (19 eyes) with a mean age of 22.7 years old (range from 19 to 25 years old) performed a computer reading task (with an accommodative demand of 2.50 D) for 30 minutes. Ocular and corneal aberrations were measured immediately before and after the task using the Visionix VX 120 (VisionixLuneau,Chartes,France) equipment. The results were evaluated for a 5 mm pupil diameter. The compensation factor was computed from the RMS values of the low order aberrations (LOA) 3rd order to 6th order aberrations, coma, spherical aberrations (SA) and high order aberrations (HOA). Results showed a decrease in the compensation factor for LOA, third order aberration and coma but others suffer no changes. It seems that there was an interaction between corneal and internal aberrations during the computer near vision. The visual system seems to adapt to compensate the changes provoked by the task, leading to a diminution of total ocular aberrations, allowing a reduction of ocular optical quality with the task less intensified.
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In pseudophakia, the eye is unable accommodate so proximal objects can be properly focused. Achieving functional vision levels relies on individual anatomical features, notably, the pupil size. This study measured the range of pupil sizes found in a population of pseudophakes, for an object placed at different distances, and modeled the optical quality associated to pupil variation. The pupil size of 58 pseudophakic eyes (age mean ± standard deviation: 70.5 ± 11.3 years) was measured using a binocular eye-tracker. The participants observed on a monitor a circular white patch subtending 5° with a cross on its center. The object was placed at 3.0, 1.0, 0.66, 0.5, 0.4, 0.33 m. The pupil size variation as a function of object distance was modelled using a linear mixed effects model. The mean and 95% confidence interval (CI) were calculated for a far object and the slope of the function, indicative of the proximal myosis. The effect of object distance on the image quality was modeled using a pseudophakic model eye for the pupil size data. The mean distance pupil sizes were 4.45 (95%CI: 2.74, 6.17) mm and the mean proximal myosis was -0.23 (95%CI: -0.53, -0.08) mm/D. The VA estimation for a distance object ranged from -0.1 logMAR for the smallest pupil to 0.08 logMAR and the near VA when mean myosis was considered ranged from 0.28 logMAR to 0.65 logMAR. These results support the importance of distance pupil size measurement for the prediction of visual performance in pseudophakia, while suggesting that myosis has a negligible impact in VA variability.
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The potential of nanosystems with combined magnetic and plasmonic properties for biomedical applications has been recognized. Magnetic nanoparticles can enable magnetic drug targeting and hyperthermia, while plasmonic gold nanoparticles ensure effective local heating (photothermia) using relatively low energies for gold excitation. Considering cancer therapy, the combination of magnetic and plasmonic capabilities in a single multifunctional nanosystem allows magnetic guidance and production of local heat, the latter promoting triggered drug release and synergistic cytotoxic effect in cancer cells (combined chemo/phototherapy).1 In this work, magnetic/plasmonic nanoparticles of nickel ferrite/gold were prepared, including core/shell nanoparticles (with a nickel ferrite magnetic core and a gold plasmonic shell) and nickel ferrite nanoparticles decorated with gold nanoparticles. In order to develop applications in combined cancer therapy, the prepared nanoparticles were covered with a lipid bilayer, these systems being able to transport drugs. The heating capabilities of the nanosystems were evaluated through the fluorescence quenching of the dye rhodamine B incorporated in the lipid bilayer upon excitation with a light source. The developed multifunctional nanosystems have shown promising results for application in combined cancer therapy (chemo/phototherapy).
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The aim of this study is to benchmark the optical properties (transmittance, absorption and dispersion) of two different types of contact lenses (daily replacement hydrogel - Hioxifilcon A and monthly replacement silicone-hydrogel - Asmofilcon A) in the visible spectra using the IAD method. Lower transmittance, lower absorption and higher dispersion were found for daily replacement contact lenses - Hioxifilcon A - than for monthly replacement contact lenses - Asmofilcon A. As diopter powers increase for both type of lenses, transmittance and absorption decrease and dispersion increases, which may have implications on the visual performance of these contact lenses.
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The aim of this study is to analyse the effect of dehydration of two contact lenses – LC - (daily replacement hydrogel - Hioxifilcon A and monthly replacement silicone-hydrogel - Asmofilcon A) on their optical properties (transmittance, absorption and dispersion). Significant differences were found between dehydration levels of Hioxifilcon A and Asmofilcon A contact lenses. Conventional hydrogel lenses dehydrate quickly, which leads to a greater alteration of their optical properties. For both materials, with dehydration reflectance increases due to scattering within the material and transmittance decreases due to increased absorption. These changes are more noticeable for daily LCs of conventional hydrogel.
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Magneto-sensitive liposomes can be obtained by encapsulation of magnetic nanoparticles into liposomes or by the coverage of magnetic nanoparticles with a lipid bilayer. The so-called magnetoliposomes make possible to explore the synergistic effect between chemotherapy and magnetic hyperthermia in cancer therapeutics. Both aqueous magnetoliposomes (magnetic nanoparticles entrapped in liposomes) and solid magnetoliposomes (clusters of nanoparticles covered by a lipid bilayer), containing biocompatible magnetic nanoparticles, have been developed, exhibiting a superparamagnetic behavior and diameters below 150 nm. These nanosystems were successfully tested as nanocarriers for fluorescent potential antitumor drugs. Drug-loaded magnetoliposomes have shown the ability to interact by fusion with models of biomembranes and to release the antitumor drugs in in vitro assays using human tumor cell lines. Fluorescencebased methodologies, including Förster Resonance Energy Transfer (FRET), emission quenching and fluorescence anisotropy, have been used as valuable tools for this investigation.
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Dynamic speckle metrology is a means for evaluating the speed of various processes in industrial or biological samples. The method indicates regions of lower or higher activity on the sample surface through statistical processing of speckle patterns formed on this surface under laser illumination. In this paper, we applied the method to study the influence of the substrate temperature on the drying process in azopolymer solutions leading to formation of thin photo birefringent polymer films. This would give the optimal temperature for obtaining smooth and uniform thin films for the shortest possible time. We recorded several sets of correlated in time speckle patterns of a transparent drop of azopolymer solution in two different solvents (water and methanol) on a glass plate illuminated by laser light. The temperature of the plate and respectively of the polymer solution was controlled by high-precision thermal stage. We built two-dimensional maps of activity at different moments and estimated the speed of drying of the polymer solution depending of the substrate temperature. This data were further correlated with the optical quality of the dry polymer thin films.
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Although the quantum theory of the optical response of individual atoms to coherent light with frequencies close to electronic transitions and the fluid equations for a gas are well known and understood from first principles, they are developed independently of each other and therefore cannot be applied directly to describe many of the quantum collective and transport phenomena that occur in cold atomic gases, especially in what regards their interaction with optical pulses and beams. Few attempts have been made to derive a consistent formalism and theory that are capable to model this type of systems, and those which exist rely on the adaptation of several ad-hoc hypothesis and simplifications, such as space and time dependent density operators. In this paper we provide the theoretical foundations and establish a formalism capable of paving the way for the development of new simulation tools and to explore new problems in nonlinear optics out of equilibrium.
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We report on the development of HiLight, a new multiphysics simulation platform for advanced photonics with interactive modules dedicated to the study of the propagation of light in multitude of spatially structured optical media, including nonlocal and nonlinear media, optical lattices with atomic gases and plasmas, among others.
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The optical interferential wedge or Fizeau wedge (FW) is a useful optical element with various applications in optical metrology, spectroscopy and laser technique. Various FW applications require knowledge of its response to illumination by a laser beam with an arbitrary wavefront. Recently, we applied the plane wave expansion method to study transmission and reflection of an air-gap FW under illumination with a Gaussian beam. The approach is based on the angular spectrum of the beam and the known FW response to illumination with a plane wave. In this study, we adapt this approach for the more general and more frequently encountered case of a FW with a non-air gap. We developed an approximate algorithm, which is applicable at small incidence angles to wedges with refractive indices different from 1 and illuminating beams with arbitrary amplitude and phase distributions. Comparison to the experiment is also provided.
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In this work, an inline sensor based on a double antiresonant hollow core fiber is proposed for the simultaneous measurement of refractive index and temperature. The fiber, consisting of four silica capillaries with wall thickness of ~1.5 μm and a cladding with a thickness of ~36.5 μm, is spliced between two sections of single mode fiber. The spectral behavior, measured in transmission, results from the combination of different frequencies which enable the discrimination between the two parameters. The sensing head is subjected to refractive index measurements using aqueous solutions with different concentrations of ethanol. For a sensor with a length of ~10 mm, and considering the lower frequency signal, the sensitivity to refractive index is 389.6 nm/RIU, whereas for the higher frequency, the sensitivity attained is 2.8 nm/RIU. On the other hand, the sensing head presented a sensitivity to temperature of 25.5 pm/K and -27.6 pm/K for the higher and lower frequencies, respectively.
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Carbon dots are promising luminescent nanoparticles which possess unique optical properties together with the simplicity of their synthesis. The revealing of their energy level structure is a crucial for further implementation in various applications from biology to photonics. This work is devoted to the investigation of optical responses of citric acid-based carbon dots with respect to the chemical environment, as solvent polarity. Small spectral shifts of the luminescent and absorption bands for CDs are observed. Assuming the PL is originated from the emission of various luminescent centers in CDs we explain these shifts by their intensity redistribution within PL band in different solvents. The redistribution leads to blue shift of PL band in non-polar solvents, while in polar solvents strong dependence of PL band on polarity value is absent.
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We present experimental data using an artificial eye in order to show how much astigmatism significantly reduces the quality of the retinal images obtained with a panoptic direct ophthalmoscope with two different magnifications (no magnification and a 6x magnifier. We used an astigmatism correcting device built by our own to see the improvement in the images in case we correct the astigmatism with this device. The images were registered with an Ipad pro. The results show that small amounts of astigmatism do not distort significantly the images with low magnification but once we introduce magnification to the system or increase the magnitude of astigmatism its correction is important, for obtaining good quality images.
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VEGA system is a petawatt (PW) laser user facility belonging to the Centro de Láseres Pulsados in Salamanca that allows developing experiments for exploring the physics of intense lasers interactions with matter. The Ti:Sapphire Chirped Pulse Amplification (CPA) based laser chain has three common front-end outputs (VEGA 1-2-3) at 1 PW, 150 TW and 20 TW respectively. This configuration, as well as the near future installation of an additional carrier envelope phase (CEP) stabilized system synchronized with VEGA front-end, opens the possibility of multiple pump-probe experiments. In this work we present the key components of this laser research infrastructure.
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The effect of photoinduced processes on CdSe/ZnS quantum dots surface on the functionality of TiO2 nanoparticles/quantum dots hybrid structures was investigated. It is shown that preliminary irradiation of quantum dots makes it possible to achieve a threefold increase in the efficiency of electron transfer from quantum dot to TiO2 nanoparticle in these structures. It has been demonstrated that photoinduced processes affect both the quantum yield of quantum dots luminescence and the reactive oxygen species generation by structures under visible light.
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Using off-the-shelf optical components a simple, compact optical polarimeter is designed for use with portable telescopes. The polarimeter is optimized for telescopes with an aperture of 10 inches and an f/10 focal ratio, which are typically used in introductory observational astronomy courses. The polarimeter can be used to measure bright standard stars that have published polarization values for the degree of polarization and position angle in the V band. Aperture photometry is used to measure the stellar fluxes on CCD images, which in turn is used to determine the Stokes parameters that are used to calculate the polarization state of a star. In using the polarimeter, students gain insight into how stellar polarization is accurately measured and they become familiar with how Stokes parameters are used in practice.
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Spectral information is characterized by multi-scaled interference, convolution and variability. Spectral lines are fragmented and diffused along the spectra. In many cases, matrix and physical effects do not allow to determine specific bands. Despite this limitation, the observed spectra contains significant amounts of information about the sample composition and characteristics, which once understood, can make spectroscopy an ideal technology for analyzing complex samples, such as bodyfluids and tissues. Breaking down and deciphering the structure of spectral information is paramount for the development of reagent-free point-of-care devices. A self-learning artificial intelligence was developed to take advantage of spectral complex information structure. It determines the relationships between composition and/or spectral features in high-dimensional space, where different sub-spaces correlate to specific constituents or characteristics. It also establishes a knowledgebase, by feature space transformations and optimizing co-variance search direction under the correct ’matrix effect’ context. An example of hemogram analysis with erythrocyte and leucocyte counts is presented to demonstrate the advantages of the developed methodology.
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Time evolution of Raman spectra depending on temperature were carried out on iron-doped photorefractive lithium niobate crystals with different Li content in the melt. The frequency shift of Raman lines are observed with time giving the possibility to calculate the saturation values of the photorefractive space charge field showing a linear decrease with temperature. Space charge field values are much lower for near-stoichiometric compsition sample comparing to near-congruent ones.
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We present the design, fabrication and optical characterization of functional metamaterials for optical sensing of Hydrogen based on inexpensive self-assembly processes of metallic nanowires integrated in nanoporous alumina templates[37-42]. The optical properties of these materials strongly depend on the environmental concentration or partial pressure of hydrogen and can be used to develop fully optical sensors that reduce the danger of explosion. Optical metamaterials are artificial media, usually combining metallic and dielectric sub-wavelength structures, that exhibit optical properties that cannot be found in naturally occurring materials. Among these, functional metamaterials offer the added possibility of altering or controlling these properties externally after fabrication, in our case by contact with a hydrogen rich atmosphere. This dependency can be used to design[43-45] and develop optical sensors that respond to this gas or to chemical compounds that contain or release hydrogen.
In this paper we present some designs for hydrogen functional metamaterials and discuss the main parameters relevant in the optimization of their response.
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A high-resolution advanced laser induced breakdown spectroscopy prototype was used to quantify lithium (Li) in lithiniferous rocks. Samples were collected from Barroso's mine (Portugal), claimed as Western Europe’s largest spodumene Li discovery. 51 samples from a reverse circulation drill were collected, one for each meter interval, dried, milled, pressed into pellets and further analyzed by laser induced breakdown spectroscopy. Quantification was attempted using either linear models based on the intensity of selected Li spectral lines or advanced chemometrics methods. The latter was very successful, with correlation coefficients of 0.97 against certified laboratory results.
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Detecting and classifying particles over a wide range of types and sizes is essential for precise air quality determination. In this study the use of optical waveguide-based particle detection is examined using finite element method (FEM) based simulations. The simulation model assumes a silicon nitride strip waveguide and is built up in 3D using the Comsol Multiphysics platform. The waveguide geometry parameters were varied to identify suitable geometries for single-mode wave guidance of the fundamental quasi-TE and quasi-TM modes. The geometries with their according effective wave indices are reported. Furthermore, the intensity and phase changes of the single-mode wave introduced by the presence of a particle are analyzed und the underlying physical effects are discussed for spherical particles of radii from 50 to 500 nm. The results show non-linear and non-monotonic behavior and give substantial input to understand basic particle interaction with waveguide structures. Furthermore, they provide helpful knowledge for designing waveguide-based particle detectors.
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In this work, 3D printing is explored as a solution for fast prototyping of optical fiber sensors with applications in power transformers. Two different sensing structures were evaluated using finite element method (FEM) analysis and were fabricated using 3D printing. The printed structures are composed by acrylonitrile butadiene styrene (ABS), a common thermoplastic polymer used in 3D printing. Attaching a fiber Bragg grating (FBG) to each structure, frequency measurements were successfully obtained for values between 20 and 250 Hz.
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Semiconductor quantum dots (QDs) are known for their unique photophysical properties and, in particular, their ability to multiphoton emission caused by recombination of biexcitons. However, the luminescence quantum yield of biexciton states is relatively low due to the fast Auger non-radiative process. Plasmonic nanoparticles can significantly accelerate the radiative rate of QDs. In this study we demonstrate the distance-controlled enhancement of the biexciton emission of single CdSe/ZnS/CdS/ZnS QDs due to their coupling with gold nanorods. We explain this enhancement as the distancedependent trade-off between the energy transfer and the Purcell effect. Our findings constitute a reliable approach to managing the efficiency of multiphoton emission over a wide span of distances.
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Lithographically-produced plasmonic structures, while offering exceptional control of light through light-matter interactions, have seen limited implementation into sensing technologies. This has been due to several factors, such as large ohmic losses and high cost of fabrication. The use of self-assembled superclusters of chemically-synthesized metallic nanoparticles has been proposed as means of overcoming some of these limitations, by exploiting their collective modes. In this work, the existence of such modes is successfully verified by 3D Raman tomography. Proof-ofprinciple experiments are also conducted to demonstrate the potential of superclusters in sensing schemes.
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Semiconductor quantum dots (QDs) are characterized by orders of magnitude higher multiphoton linear absorption cross-sections compared with conventional organic dyes. Combined with the QD photoluminescence quantum yield approaching 100%, this fact opens great prospects for the twophoton functional tumor imaging with QDs tagged with highly specific recognition molecules. Single-domain antibodies (sdAbs) or “nanobodies” derived from lamas are the smallest high-affinity recognition molecules, which may be tagged with the QDs thus permitting not only solid tumors multiphoton imaging but also rare disseminated cancer cells and micrometastases in the depth of the tissue to be detected. Additionally, unique photostability of QDs enables signal accumulation and significant enhancement of the sensitivity of routine biochemical and immunohistochemical assays to be obtained when the conjugates of QDs, instead of organic dyes, are used.
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We report on the effects of surface organic ligands on the properties of CdSe/ZnS/CdS/ZnS quantum dot (QD) solutions and condensed films. Hexadecylamine, octylamine, hexadecanethiol, octanethiol, thiophenol and inorganic ZnCl2 were used as the QD surface ligands affecting their properties. Here, we analyze optical and electrical properties as well as surface quality of thin films fabricated from the QDs bearing different ligands on their surfaces. We have found that the use of thiol ligands results in QD-films with a uniform surface, sufficient quantum yield and resistance, thus approving their relevance for the use as electroluminescent layers in light emitting diodes.
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Light-matter coupling between the molecular dipole transitions and a confined electromagnetic field provides the ability to control the fundamental properties of coupled matter. The use of tunable optical microcavities for electromagnetic field confinement allows one to affect the coupled state properties in a controllable manner, whereas the coupling strength in this system strongly depends on the transition dipole moment and a mode volume of the cavity. In this study we have demonstrated controllable emission of Rhodamine 6G organic molecules with relatively low and unoriented dipole moments in a strong coupling regime by placing them into a tunable Fabry-Perot microcavity.
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Quantum dots (QDs) are fluorescent semiconductor nanocrystals with a high photostability, wide absorption spectra, and narrow, size-tunable emission spectra, which make them promising nanolabels to be encapsulated in microcarriers used as bioimaging and theranostic tools. Here, we describe an approach to the optical encoding of polyelectrolyte microcapsules with the prepared stable water-soluble QDs and key stages of surface functionalization of these microcapsules with cetuximab, humanised monoclonal anticancer antibody. Obtained conjugates demonstrate the specificity and efficiency of the engineered system as a cancer cell–targeted tracing tool that could be used for cancer diagnosis, treatment and monitoring of cancer therapy.
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An electrodynamics model of a fiber-optic hydrogen sensor with a taper in a special photonic-crystal fiber coated by a nano-scale palladium film is proposed. The transmission spectrum of the sensor is explained by the interference and mutual transformation of local modes in the taper. As a result, the model contains 3m+1 free parameters, where m is the number of local modes taken into account. The parameters are determined by the least square method from the experimental transmission spectrum. This approach allows us to determine the dispersion characteristics of a nanoscale palladium film in a hydrogen atmosphere and optimize the taper from the standpoint of maximizing the sensitivity of the sensor.
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The manufacturing of inline Fabry-Perot cavities in standard single mode telecommunication optical fiber is presented. The procedure consists in splicing two optical fiber pigtails, one of them with a micro-drilled hole in its tip, creating an air bubble inside the structure. The initial hole is obtained using near infrared radiation from a Q-switch Nd:YAG laser to open 5-10 micrometers deep cavities by laser ablation and plasma formation processes, and a standard splicing machine is used to fuse the two fibers. The length of the obtained cavities lies around 80-110 micrometers. Preliminary tests as a strain sensor are presented.
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The assessment on the ability of brain-computer interfaces (BCIs) to acquire electroencephalographic (EEG) data in situations of luminous glare is presented. Dazzling is typically a temporary deleterious effect on the ability to see or concentrate due to glare. The potential of BCIs was evaluated by defining a set of strategies involving the illumination process, EEG signal recording and analysis. N-back, a continuous performance task commonly used in cognitive neuroscience was used to test the attention under the effect of dazzling, in parallel with EEG signals acquisition. Statistical data analysis allowed to show the potential of this technique.
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In this work, we describe how, from the early stages of device characterization, it is possible to evaluate the suitability of a given device design for the long life-time demand of a challenging deployment environment (uncooled, non-hermetic operation). Understanding the reasons for non-compliance and device failure, as well as their clear association with the device fabrication procedure steps, greatly helps to systematically improve the device quality yield for volume production.
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Neutron optics is the branch of quantum physics devoted to the study of the optical properties of slow neutrons and their behavior as wave-particles. Slow neutrons beams (with typical energy the order of 0.025 eV, known as thermal neutrons, and also smaller) can propagate confined in guides of various transverse dimensions, longitude and geometries, under total internal reflection conditions, like in the case of classical optical waveguides. We study the properties and possible applications of neutron waveguides with small transverse dimensions. In particular, we have implemented a new algorithm to simulate neutron beams as they are confined in particular waveguides. The results, obtained from a new analytical formalism, are compared with standard numerical methods as the FDTD and, then, enhance the feasibility for recreating the beam structure as the later propagates inside the waveguide.
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Holographic gratings stored in low-toxicity photopolymer, Biophotopol, have been analyzed to achieve stable and efficient holograms. A curing process allows the hologram stabilization, but at the same time, it could produce a diffraction efficiency (DE) reduction. Here, a detailed low-cost LED curing protocol is shown to stabilize over time 1205 l/mm transmission holograms, and at the same time, a 33% DE increment (with respect non-curing holograms) have been demonstrated. Finally, to obtain a better understanding of DE change, a theoretical fit of our experimental result, based on Kogelnik’s coupled wave theory was carried out and discussed.
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Nowadays, there is an increasing concern about the use of less harmful techniques to the environment, and about road safety in Transportation Engineering. Heterogeneous photocatalysis based on the application of semiconductors materials onto asphalt mixtures is a promising technology because it can mitigate air pollution and road accidents. The functionalized asphalt mixtures with photocatalytic capability can degrade pollutants, such as damaging gases and oil/greases over their surface from specific reactions triggered by sunlight photons, providing significant environmental and social benefits. In this communication, a brief review of photocatalysis applied in asphalt mixtures will be presented.
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We discuss the use of pairs of optical masks for setting tunable optical focalizers and for implementing controllable absorption masks. For phase-only masks, one element of a given pair has a complex amplitude transmittance that is equal to the complex conjugate of the other element. For the absorption masks, we use a suitable attenuation offset. Then, from the attenuation offset value, one element has the opposite absorption profile that the other element. These methods are useful for generating varifocal lenses, governable prisms, tunable axicons, controllable axilenses, for tuning field depth, and for controlling Super Gaussian beams.
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In this paper, we demonstrate the use of simple one-step chemical route using oleylamine as reducing agent to obtain colloidal Sc2O3 nanoparticles doped with europium ions. By changing the condition of synthesis we were able to modify dual mode single-photon induced luminescence of Eu2+/Eu3+ upon UV excitation. Additionally, non-linear optical properties of the synthesized nanoparticles have been studied.
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Second-harmonic generation frequency-resolved optical gating (SHG FROG) is one of the most commonly chosen setups for pulsed light measurement and is characterized by a high sensitivity and robustness1,3 . In this article, a new implementation for a compact and portable LEGO SHG FROG setup is presented with the goal of measuring light pulses from an 800 nm laser at different experimental stages for diagnostic and validation of results in the VOXEL laboratory, at IPFN. With a “plug and play” cased setup, complete with LEGO two-axis tilters, holders and an overall assembled structure we hope to achieve a compact solution for a fast pulse characterization and easy mobility in between different laser stages. This low-cost customizable solution also aims to encourage academic institutions to introduce LEGO elements to multiple photonics experiments for an economical and viable approach.
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We present separation of fibre Bragg grating wavelength reflections in a multicore fibre with an even peak wavelength distance between reflections in the multiple cores of a single cross-section plane. The inscription is achieved simultaneously in all cores by applying a bend in the fibre, and thus inducing a different variation of the effective refractive index in each core. Such method for wavelength multiplexing would enable the interrogation of multiple sensors signals delivered by a single channel, e.g., without the need of a fanout device or a multichannel spectrometer.
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New luminescent materials have a wide range of applications in either chemistry, biology or electronics. The study of nontoxic and inexpensive luminescent materials is the key to a sustainable future. Luminescent solar concentrators are the example of a very promising application of luminescent materials and the optimization of the optical conversion efficiency of the glasses produced is essential for the development of the luminescent solar concentrators - for this it is necessary to determine the refractive index of the different glasses. There are many existing techniques for determining the refractive index - the current situation regarding systems that perform this type of measurements is that there are simple systems for low accuracy and complex systems for high accuracy of results, and the middle ground is often left unexplored. For the manufacture of luminescent solar concentrator glass, it is important to have access to a simple refractive index measurement system with an uncertainty of less than 1%. The system should be simple to implement, cost-effective and automated to allow a typical user to obtain the desired information on optically simple samples. Two independent techniques for measuring the refractive index are approached, one using the lateral displacement of a laser beam and the other the interferometric pattern obtained by an interferometer.
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LiDAR technology is bounded with great expectations. This is a result of the high market prospects from several industries (notably the automotive) as well as LiDAR being a key enabling technology for automation. We will drive along the current two main avenues of LiDAR, targeted to autonomous driving. We will stop at minute technicalities of LiDAR implementations. However, occasionally we will also rise high, to get an eagle-eye view of the bigger picture. We discuss why there will not happen a one-single-expensive-LiDAR-fits-all-scenarios and why a several-cheap-complementary-LiDARs alternative is more rational. We discuss several aspects in which LiDAR changed our understanding of the landscape as well as the high impact it will have in society (economic and quality of life). Automotive LiDAR comes in an age where the societal focus is changing from private ownership to pay-as-you-use-services, and where personal responsibility will be gradually replaced by corporate liability. We will introduce some minor contributions from the Physics Centre of Minho and Porto Universities (mutual interference between commercial sensors; data processing in timing the back scattered LiDAR signal). And by the end of the route, we drop off the partaker to explore uncharted territory on its own.
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In this paper, a correlation between conditions of synthesis of manganese-containing cadmium sulfide or zinc sulfide quantum dots and their optical and magnetic properties is analyzed. The method of electron paramagnetic resonance was used to study distribution of manganese ions in nanoparticles and the intensity of interaction between them depending on the conditions of synthesis of nanoparticles, the concentration of manganese and the type of an initial semiconductor. Luminescent properties of nanoparticles were studied, the results were correlated with the concentration and position of manganese ions and the EPR data.
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Optical microbubble resonators are among the highest sensitivity optical sensors. In the context of its application in the detection of water micro contaminants, in portable systems, their interrogation must be made by tracking the resonant wavelength peak position with the highest accuracy possible, at a reasonable cost. In this work different laser sources and scanning methods were tested and compared, aiming the development of a portable prototype. Each tunable laser source, was evaluated using a C2H2 Gas cell, which provided an absolute wavelength reference. Light transmitted through the cell was recorded using a photodetector and a software controlled feedback loop, enabling locking into selected reference peaks. Three distinct scanning methods were tested and compared for each laser source: large and short-range laser scanning and external waveform dithering, from which minimum standard deviations of 20, 0.18, and 0.07 pm, were obtained, respectively.
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A low-computational intensive laser control approach is proposed for implementing an embedded control system, using pattern recognition by relevant principal component analysis for laser induced breakdown spectroscopy applications. The laser energy is directly related to the resulting spectral pattern and is determined by iterations in the feature space. Results show that single shot iterations until optimum energy can be significantly reduced by pattern recognition. A performance benchmark with minerals, alloys and pellets from material collected from a drill demonstrated an average of 50% improvement, significantly reducing sample deterioration and improving measurement safety.
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Use of aspheric mirrors is common practice to design astronomical telescope with just a few optical elements. For an example in the most preferred telescope optical design, Ritchy Chretien (RC) both primary and secondary mirrors are hyperbola. Nowadays large telescopes are being built using small mirror segments, however, making aspheric off-axis mirror segment is a challenge. We have conducted a study in which we have explored a possibility to mimic aspheric hyperbolic primary mirror by making use of smaller spherical mirror segments. In this paper we present results of our study on designing an RC type telescope optics for an 10m class optical-NIR telescope
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The method of creating microscale luminescent film materials with controlled optical properties from anisometric analogues of Ln(DBM)3Phen and Ln(bzac)3Phen complexes (Ln = Eu, Tb) is proposed in this paper. Within the framework of this research, we fabricated original films, which are highly uniform and transparent. An important advantage of these films is their high photostability and potential for applications as reusable luminescent sensors and light converters.
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In several domains, we found increasing demands to assess cognitive workload and fatigue. This article presents part of the work produced towards the implementation of an integrated system composed of an Electroencephalography (EEG) device and an eye-tracker, focusing on the optical devices. Pupil dilation was found to be related to task difficulty and cognitive workload, where dilation of the pupils indicate greater mental workload. This and other optical parameter can act not only as complement to the EEG system but also as a cross-validation tool. Lenses adjustments and calibration process of the eye-tracker are discussed along with preliminary results from pre-test of the experiment protocol.
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Mixed saliva is a unique biological liquid that has a great opportunity for use in fundamental research and in the early diagnosis, prognostication, and monitoring of post therapy status. The study of biochemical composition of mixed saliva and its properties in normal samples and samples from donors with various diseases may reveal some important characteristics for noninvasive diagnostics. In biomedical practice mixed saliva is investigated by various biochemical, chromatographic and optical methods. Optical methods are mostly used due to their high sensitivity, speed, noninvasiveness, low cost, etc. In our study samples of mixed saliva from a healthy patients were studied by electrophoretic light scattering technique. During the measurements protein particles in saliva migrate to the opposite charge electrode and start to separate into its constituent components due to differences in their electrophoretic mobility. Experimental results of determination of electrophoretic mobility of mixed saliva from healthy donors and its interpretation are considered.
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Today, the number of diseases related to the immunity of the human body is increasing. Diagnosis of such diseases is of paramount importance in medical practice. It is possible to diagnose diseases of human immunity by analyzing human biological fluids. In this paper, we consider the method of laser correlation spectroscopy and optical microscopy for the study of the self-organized blood serum films for medical diagnostics purposes. Experimental results shown that, the addition of the toxoid in the blood serum changes the structure of the film and dynamics of agglomerating and the size of the agglomeration. Thus, in this work, we have shown that employing the methods of laser correlation spectroscopy and optical microscopy of dehydrated films of biological fluids, it is possible to analyze the state of human immunity.
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In modern medicine methods for studying structural properties of biological fluids are very demanded. However, existing methods for blood and other biofluids analysis do not allow mass studies and dynamics considerations. In this case, medicine can use a number of optical methods, which usually are able to perform express and simpler types of measurements. Our previous studies have shown that methods based on light scattering, such as laser correlation spectroscopy, are useful for structural analysis of biological fluids, in particular blood serum and saliva. In this work, we discuss an original hardware-software complex based on laser correlation spectroscopic technique. We present an original setup and algorithm of data analysis to study compounds of biofluids. The testing of the hardware-software complex have shown high sensitivity and accuracy. The further applications in medicine are also discussed in this work.
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A single shot automatic optical inspection system for evaluating the projection distance, astigmatism, field curvature and geometric distortions of a virtual image created by a Head-Up Display (HUD) prototype is presented. The system uses plenoptic or light-field imaging. Although results are only presented for a Augmented Reality (AR)/Mixed Reality (MR) HUD application, the inspection workflow is also applicable to a plurality of other optical systems for AR, MR, and Virtual Reality (VR) applications. The evaluation of the quality of a latent image (in most cases a virtual image) is necessary in all these systems, both for product development as well as for end-of-line production quality control. Therefore the results here presented should have an appeal for a broad readership.
For the HUD virtual image, the projected distance distribution functions are presented, for two selected patches in the FOV (Area 1 and 2). These are well described by Gaussians. As representative values, we obtained a mean projected distance of 0.15 ± 0.02 (horizontal details) and 0.03 ± 0.02 (vertical) Diopters, for Area 1, and 0.33 ± 0.04 (horizontal) and 0.03 ± 0.02 (vertical) Diopters, for Area 2. The estimated astigmatism is 0.12 and 0.30 Diopters, for Areas 1 and 2, respectively. When expressed in meters, the projected distances are 7 1 (horizontal) and 28 9 (vertical), for Area 1, and 3.1 ± 0.4 (horizontal) and 30 ± 10 (vertical), for Area 2. The estimated astigmatic difference is 21 and 23 meters, for Areas 1 and 2, respectively.
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Dark matter is a key ingredient to physical cosmology, and one of the mysteries of modern science. Among a variety of possible candidates which have been explored in recent decades (such as WIMPs and WISPs), the axions are the most promising constituents of dark matter. These hypothetical particles have been proposed to solve fundamental problems of charge- parity (CP) invariance and their discovery could therefore solve two important problems in cosmology and in particle physics. The axions, and axion-like particles, have been actively searched without success since the 80’s of the last century, using both laboratory experiments and astrophysical observations. In recent years, it became clear that the axions, if they exist, could be actively produced by intense laser pulses in magnetised and unmagnetised vacuum, and that the axion field could become unstable under the action of intense laser beams. Alternatively, the signature of axions could possibly be found in the dispersion relation of electrostatic waves in strongly magnetised plasmas, due to the formation of the axion-plasmon mode. This new mode could be excited by intense laser pulses in a plasma. In the present work, we consider different configurations leading to the excitation of axions by intense laser pulses, and consider propagation both in vacuum and in plasmas. A discussion of possible experimental arrangements, using the available laser technology is included.
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Holography is a part of optical physics that deals with the capability of producing three-dimensional images using coherent light sources, namely lasers. Key phenomena in optical physics – interference and diffraction – are directly behind its remarkable characteristics. The main objectives of this work follow along two major lines: i) the development of experimental approaches for hologram production using simple and inexpensive setups, and ii) the production of holograms effectively capable of illustrating important optical instruments, physical principles and/or effects. This is for the purpose of engaging students in the study of Physics, and to reinforce the yet modest presence of optical physics (including interferometry) and modern physics in undergraduate physics courses in Angola. Here we present experimental results in hologram production obtained with a versatile setup based on a single-frequency diode-pumped solid-state laser. This is aimed at testing several hologram recording geometries and concepts prior to developing more simplified setups based on inexpensive diode lasers. We also highlight a set of published works on applied holography that show how interference and diffraction phenomena are vital to many fields of applied physics, and how holography can be applied in different areas of science, technology and industry.
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