This PDF file contains the front matter associated with SPIE Proceedings Volume 12428, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

A fully automated solution for designing metalens/metasurface systems has been developed to optimize the parameter values of each meta-atom on each metasurface based on the given inputs and desired targets. Unlike traditional design approaches, which are based on a given phase profile for a particular incident condition, inverse design can generate the optimum layout and its simulation results automatically based on a limited set of inputs from designers. The knowledge required of designers is minimized significantly. Hence, designers at different levels of expertise, including undergraduate students, can use this software solution to design metalens systems quickly.

The Korea Astronomy and Space Science Institute is developing GrainCam as a candidate payload for NASA's Commercial Lunar Payload Services (CLPS). GrainCam is a suite of two light field cameras: one of which is called SurfCam to observe the uppermost regolith on the lunar surface, and the other is LevCam to observe levitating dust over the lunar surface. This paper includes SurfCam's optical design and related analyses. The main goal of SurfCam is to get knowledge of the regolith on the lunar surface and obtain 3D images of the micro-structures through image processing with a micro-lens array (MLA). SurfCam consists of 1 cover glass and 12 spherical lenses. All lenses use space-qualified glass material to carry out a one-lunar-day mission on the moon and are designed to keep the required performance at the operating temperature of -20 ~ +60°𝐶. SurfCam based on the design works will conduct various tests to verify the overall performance through assembly and alignment.

Many different applications require the precise acquisition of the spatial intensity distribution of a light source. Examples are measurements of M2 (beam quality parameter), numerical aperture (of an optical fiber), or light source characterization. The presented work shows the development and validation of a photonic instrument for spatially resolved precise light power measurement at different distances. The instrument consists of a XY-stage with a calibrated detector. It is located in a dark room with an additional black carpet to reduce stray light even from the surrounding. We designed and built a fully automated measurement device including data processing. Different sources can be measured at a freely selectable distance (Z direction) between source and detector. The detector is a photodiode with a transimpedance amplifier (calibrated). In front of the detector, an aperture ensures a precise XY resolution. The scan area is 52 mm in X and Y direction with the smallest step size of 0.2 μm and a repeatability error of less than 0.5 μm. The aperture is currently limited to ≥ 0.4 mm (diameter) due to mechanic reasons at our lab. From repeatability testing, we calculated the accuracy of the current instrumentation: a 2s experimental standard deviation of less than 0.8 %. Such a photonic instrument is the base for precise optical beam profile measurements.

We propose a novel 2-in-1 pattern projector, which consists of a Dot projector and an LC diffuser. The LC diffuser is made of switchable Microlens Arrays (MLA) based on geometric phase. The LC diffuser can switch between “no lens power” and “MLA” mode. In “no lens power” mode, the Dot pattern is not affected by the LC diffuser. In “MLA” mode, the focused Dot pattern is “blurred” by the MLA, which generates the Flood pattern. The eigen mode of geometric phase MLA is carefully designed to achieve polarizer free modulation. We implement this novel modulation concepts with the world smallest and 1st ever reflowable LC cell. We made a record of 3x3mm LC cell with our in-house IJP system. The optical efficiency is over 95%, and the switching time is less than 5ms.

Curved imaging sensors bring significant size, weight and cost reduction to imaging systems while mitigating off-axis optical aberrations, as opposed to current flat sensors. Unlocking these key features has captured the interest of major players over the last two decades. SILINA has been developing a CMOS Image Sensor (CIS) curving process, which adapts to various sensor characteristics. This enables to maximize the optical performance of every single imaging system. We have demonstrated the manufacturing of curved CMOS Front-Side Illuminated (FSI) and Back Side Illuminated (BSI), opening a new area of compact, fast, wide-angle and high-resolution optical lenses. This new degree of freedom offered to optical designer can significantly simplify optical systems through a significant improvement of the optical performance while simplifying the system architecture in many different ways. The field of view (FOV), the contrast, the aperture can be increased while optical aberrations can be minimized. At the end, the different costs related to manufacturing, metrology, integration, and alignment are reduced. This is of great importance for applications requiring compact and high resolution lens, notably in low-light environment. To quantify the gain brought by curved image sensor for smartphone camera lens, we are performing several comparative optical lens designs. We compare traditional flat-image sensor based camera lens to camera lens optimized specifically with a curved image sensor. In this paper, we present the result obtained on wide-angle smartphone camera lens design considering a spherical concave image sensor. We compare the optical characteristics and performance with a reference optical design using a flat image sensor. We discuss the various benefits in terms of optical performance and Z-stack reduction.

The latest changes to the UL-217 and UL-268 standards challenge current and existing smoke detectors and necessitate the development of better performing devices that are more sensitive towards polyurethane fires and simultaneously more resistant to nuisance alarms. Possible design strategies that include multi-color or multi-angle scattering techniques further increase the complexity and requirements for new detectors. Optical simulation is a key instrument for the design and development phase to improve the performance of photoelectric smoke detectors to meet the more stringent requirements. Going hand in hand with vertical manufacturing that allows detailed knowledge and control of each component the goal was to build an optical model that strives for achieving qualitative and quantitative performance predictions. This model starts from the optoelectronic component level and goes up to the fully assembled smoke module. We tested the optical model against experimental data of an existing photoelectric smoke detector and improved it to show convergence between simulated and experimentally measured data. On this basis, we investigated and optimized key optical design parameters to achieve better signal-to-background levels that pave the way for enhanced smoke sensitivity and an easier discrimination between smoke sources and non-hazardous nuisance sources. The optimization of interaction volumes, wavelength dependent scattering angles, and surface features that directly control the path of light with the consideration of manufacturability and robustness against assembly tolerances was of particular interest. The outcome of this process is an optimized dual color smoke detector whose performance is consistent with the predictions of our optical model.

This paper discusses a high sensitivity quantitative method to efficiently detect the defect existence and allocate the impurity down to single micron level. This methodology by nature only enhances the defects within the signal path no matter on the optics surface, in the coating or inside the glass material, which fundamentally helps on high contrast optics like the AR/VR metrology lens which mimics human eye’s sensitivity, or deep space observation optics or biology imaging system.

We propose an imaging system and method for leakage detection in the consumer electronics manufacturing industry that uses Schlieren imaging with a collimated beam emitted from a white/color LED as a back illumination light to image, locate and characterize a flow of pressurized gas with a refractive index different than that of ambient air from certain leak areas of a sealed device under test (DUT). In particular, the Schlieren imaging system includes a collimated light, a knifeedge spatial filter and a 4F telescopic imaging system used to create an image of the DUT, which is pressurized and monitored for leaks. When a leak is present and in the monitored plane of the DUT, contrast variation reveals the presence, location, and characteristics of the leak. For example, we can evaluate a waterproof/leakproof mobile device for leakage between layers of modules, such as leaks in the housing of a waterproof electronics case. This detection method can allow identification and characterization of leak points via visual identification, where we use a fiber-coupled LED as a light source to create high quality collimated light for the best Fourier filter effect for a 4F imaging system. Our application shows that LED light has sufficient chromatic quality to act as a light source for a Schlieren imaging system with high sensitivity.

CEA aims at developing a compact 1550 nm Frequency Modulated Continuous Wave (FMCW) LiDAR on chip. In this paper, individual demonstrators, corresponding to three main components of a LiDAR (Light Distance And Ranging) system, are combined in a test bench: a FMCW laser source, an emission and reception Optical Phased Array (OPA) and an optical heterodyne detection module. Each component has been individually tested, but also evaluated in order to derive the system performance of a complete LiDAR. A test platform has been developed to calibrate an OPA fabricated at CEA platform, either in emission or in reception mode. The tested OPA includes 256 channels based on grating antennae, with 1.5 μm pitch and 256 thermo-optic phase shifters. More recently, this platform has been completed with a FMCW interferometer, where the FMCW LiDAR detection can be evaluated through a mixed propagation setup, composed of optical fibers and free space. Then, the OPA may be inserted into this setup. Therefore, the optical fiber FMCW interferometer has been optimized to detect the lowest signal (typically less than one hundred fW) and to estimate the signal-to-noise ratio (up to almost 30 dB) with low noise photodiodes. Performance has been compared to theoretical predictions. Then, our custom OPA is included inside this experimental setup in a free space propagation environment. The performance measurements extracted from the spectral analysis are in agreement with the expectations.

Photonic Doppler Velocimetry (PDV) systems measure velocities in shock physics experiments on novel materials. In many experiments, diffusive materials limit the amount of Doppler signal collected, which degrades the measurement. Increasing the laser power comes with a cost when many channels are supplied at the same time and could damage some sensitive surfaces. The use of a multimode fiber with a 62.5 μm core diameter in the collimator or focuser brings more signal into the interferometer but, on the other hand, the multimode behavior of the fiber reduces interference contrast. PDV systems with 62.5 μm multimode fiber were tested at 1550 and 532 nm on a test-bench at low velocities. The interference amplitudes are discussed according to tilt angle and for different surface qualities. The trends differed with wavelength. A multimode system was also tested under real conditions during a ramp compression experiment with velocities greater than 100 m/s. Practically, the use of multimode fibers greatly facilitates probe alignment, especially at 532 nm. Furthermore, 532-nm singlemode fiber are rapidly limited in terms of their optical power. For the two wavelengths tested, the high-speed measurements show clear interference fringes with at least the same amplitude level as with singlemode PDV systems. The benefits of multimode PDV systems appear clearer for highly diffusive surfaces and when probe alignment cannot be guaranteed. At 532 nm, better results are expected using fibers with a core diameter in the range of 20 μm if the optical components become available.

A novel transmissive-reflective beam scanner operating around 1550 nm wavelength has been demonstrated using two commercial wire grid polarizers (WGPs) with transmission axes offset by 45°, surrounding a latching garnet 45° Faraday rotator. Light in the system undergoes three 45° polarization rotations, resulting in two reflections inside the cavity between the two WGPs before being transmitted by the rear WGP. The two reflections inside the device facilitate beam steering in a transmissive layout (output beam emerging from the opposite side of the input beam). Polarization-resolved individual-component characterizations were performed for several WGPs and for the Faraday rotator to determine optical properties such as transmission efficiency and the polarization purity of the transmitted or reflected beams as a function of incidence angle to the optic, for multiple incident linear polarization states. This allowed us to both select the WGPs best suited to act as polarizing beam splitters in the system and to use the angle-resolved component data to predict the total transmission efficiency of the beam scanner as a function of front polarizer tilt angle (which in our geometry is half of the beam deflection angle). We then compared the predicted scanner efficiency with the measured transmission efficiency of the prototype beam scanner. The scanner maintained a transmission efficiency over 70% for beam deflection angles between ±45° (a 90° symmetric beam scan area) for a vertically oriented incident linear polarization state.

Additive manufacturing has a great potential for modifying optics in a way that new functions, for example individual light distributions, could be realized by modifying the optical surface. The functionalization of the curved surface by multijet modeling is the goal of the 6D printing project (6D AF) at the Center of Optical Technology, Aalen University. To combine the coordinate systems of the printing unit, the printing table and the metrology unit a new photogrammetric position measurement system is developed and presented. First results of the accuracy in three axes are show and the improvement in motion is demonstrated.

It is presented in this work a description of an optomechanical setup to be used for the characterization of planar photonic chips. The system allows the fine tuning of an optical fiber position on an input grating, controlling its XYZ position and its angle of incidence. A similar configuration is used for the output extraction, while a fiber array can be used an alternative to monitor multiple output channels. Such a configuration can be useful for characterization of arrayed sensing devices or Optical Phased Arrays. The system can be used in the visible range and in the IR spectrum as well, provided the input light source is changed. All the setting are controlled manually, and it is prepared to easily perform a sequential analysis of a set of identical circuits, fabricated in a parallel configuration on the same chip. As most of the components are individually and commercially available thought the Thorlabs website, the set up can be easily replicated, so all the system designs are made available in Open Access modality in SolidWorks format. Examples of characterization process and the obtained results are reported to demonstrate the use of the system and to support a tolerance analysis.

Fourier-plane optical microscopy is a powerful technique for studying the angularly-resolved optical properties of a plethora of materials and devices. The information about the direction of the emission of light by a sample is extracted by imaging the objective back focal plane on a two-dimensional detector, via a suitable optical system. This imaging technique is able to resolve the angular spectrum of the light over a wide angular field of view, but typically it doesn’t provide any spectral information, since it integrates the light intensity over a broad wavelength range. On the other hand, advanced hyperspectral imaging techniques are able to record the spectrum of the transmitted/reflected/emitted light at each pixel of the detector. In this work, we combine an innovative hyperspectral imaging system with Fourier-space microscopy, and we apply the novel device to the characterization of planar organic microcavities. In our system, hyperspectral imaging is performed by Fourier-transform spectroscopy thanks to an innovative common-path birefringent interferometer: it generates two delayed replicas of the light field, whose interference pattern is recorded as a function of their delay. The Fourier Transform of the resulting interferogram yields the intensity spectrum for each element of the microscope angular field-of-view. This system provides an angle-resolved hyperspectral view of the microcavities. The hyperspectral Fourier-space image clearly evidences the cavity modes both in photoluminescence and reflection, whose energy has a parabolic dependence on the emission angle. From the hyperspectral image, we reconstruct a 3D view of the parabolic cavity dispersion across the whole Fourier space.

The Computed Tomography Imaging Spectrometer (CTIS) is a snapshot hyperspectral camera based on computational imaging. Typical designs use a Keplerian beam expander to limit the imaged scene and decrease the incident ray angles. We have found that the use of a Galilean beam expander instead can be beneficial. Often a smaller system with a better optical quality is achievable with the disadvantage of a vignetted image. Results of a comparison between both designs based on a prototype will be shown. Furthermore, we present our miniaturized CTIS system, which uses the Galilean design.

We develop a special type of imaging multicolor ellipsometer to map big area thin layers or multilayers on rigid or flexible substrates. In thin film production, layer thicknesses, micro-structure, composition, layer optical properties, and their uniformity are important data. Scanning ellipsometers with conventional collimated beams measure with high precision but the mapping time can be very long. We developed expanded beam ellipsometry to map rapidly the polarization state changes after reflection from bigger surfaces [Horváth, Z Gy; Juhász, G; Fried, M; Major, C; Petrik, P, Imaging optical inspection device with a pinhole camera, patent WO2008142468A1]. Ellipsometric data of large areas can be collected a couple of 10 times faster compared to the “traditional” scanning methods. The aim of this work is to make prototypes for this optical mapping using only cheap parts: tablet, monitor, big screen TV and a pinhole camera using a CMOS Sensor with Integrated 4-Directional Wire Grid Polarizer Array (Sony's IMX250MYR CMOS) as detector. We present the first results of mapping the thickness on different samples.

Lidar technologies have been investigated and commercialized for various applications such as autonomous driving and aerial vehicles. The pulsed time of flight and frequency-modulated continuous-wave lidars are the two common lidar technologies that dominate. As an alternative to the available lidars, we developed the phase-based multi-tone continuouswave (PB-MTCW) technology that can perform single-shot simultaneous ranging and velocimetry measurements with a high resolution at distances far beyond the coherence length of a CW laser, without employing any form of sweeping. The proposed technique utilizes relative phase accumulations at phase-locked RF sidebands to identify the range of the target after a heterodyne detection of the beating of the echo signal with an unmodulated CW optical local oscillator (LO). Upto-date, we demonstrated that the PB-MTCW lidar could perform ranging ×500 beyond the coherence length of the laser with <1cm precision. Here, we implement machine learning (ML) algorithms to the PB-MTCW architecture to improve the ranging resolution, as well as to provide a solution to multi-target reflections using tone-amplitude variations. We used four different training schemes by utilizing the acquired RF tones and phases from simulation results, experimental results, and their combinations in a convolutional neural network model. We demonstrate that the ML algorithm yields an average mean square error of ~0.3mm compared to the actual target distance, hence enhancing the ranging resolution of PB-MTCW lidar. It is also shown that the ML algorithm can distinguish multiple targets in the same line of sight with a 98%±0.7% success rate depending on the targets’ reflectance and distances.

The detection of ammonia and similar gases over a wide range from a few Parts Per Millions (ppm) to 10,000’s ppm in a single sensor is important for industrial applications. We are exploring Vapochromic Coordination Polymers (VCP) specifically Zn[Au(CN)₂]₂, developed to achieve fluorescence when exposed to NH3. At high concentration of ammonia under UV stimulation VCP spectrally shifts its fluorescent peak from 470nm to 530nm while the intensity grows 3~5X. We use a 405nm laser diode excitation source which provides a narrow (4nm) stimulation clearly separated from the spectral peak. Focusing the emission on a USB portable spectrometer (430 to 700nm) at concentrations <1000 ppm of ammonia there is almost no peak wavelength spectral shift or intensity change and only subtle fluorescent spectrum alterations. To detect first we create a method that gives unique values over the range 1- <1000 ppm by dividing the spectrum into 10 nm bins, integrate the emission in each bin, relative to that of 0 ppm exposure, then sum all the bins (Sum of Integrated Emissions, SIE). The key analysis point is to note that the way the spectrum changes in each wavelength bin varies at different ammonia ppm exposures. SIE gives excellent sensitivity between 0-50 ppm and <400 ppm, but poor accuracy in the 100-500ppm range. Using the SIE to identify measurements in that region we switch to a second metric, Limited Range SIE, that covers only the 430-470nm bins but for 100-500ppm gives an accurate linear response. This shows that in many spectral fluorescence cases in the region where the longer wavelength peak begins to dominate looking at regions outside of the peak maximas is more accurate than including those within the unexposed to saturated exposure (eg ammonia) peak range. By creating a model assuming the fraction z of 0ppm and saturated spectrum are linearly combined we fit the measured spectrum using regression analysis to obtain the z value for all ppm measurements which show what is going on in the VCP conversion.

Several environmental trace gas species and toxic chemicals or warfare simulants have fingerprint spectral signatures in the mid-infrared region of the spectrum. For instance, methane, nitrous oxide, and water vapor are critical greenhouse gases relevant for environmental sensing. In contrast, Sarin is one of the most lethal warfare agents that is a highly toxic synthetic chemical organophosphorus compound, which is of interest in defense and security sensing applications. Due to complex chemical structure and significant absorption and collision cross-section, the molecular linewidths of such chemicals can cover a broad range of spectral widths in the mid-infrared region. Detection of such molecules in the mid-infrared region is sensitive, which requires broadly tunable sources and appropriate spectral resolution in detection schemes. We show a rapid detection methodology of atmospheric bands of trace gases in the 7 μm to 8 μm region, which also coincides with the fingerprints region of several hazardous chemicals. Methane absorbs strongly in the wavelength range of 3 μm to 8 μm, and nitrous oxide has absorption from 5 μm to 8 μm. We use molecular rotational-vibrational transitions of carbon and nitrogen trace species to demonstrate well-resolved peaks in the spectral region of 6.88 μm to 7.6 μm for detection. The detection was performed by a continuous wave multiplexed quantum cascade laser source capable of an ultra-wide tuning range from 6.88 μm to 11.05 μm.

We report on the detection of nitric oxide using an Interferometric Cavity-Assisted Photothermal Spectroscopy (ICAPS) gas sensor in combination with a DFB-QCL emitting at 1900 cm^-1 as excitation source. In ICAPS, a probe laser is coupled to a Fabry-Perot interferometer acting as an optical transducer of thermal effects. A wavelength modulation approach of the probe diode laser was employed, to actively lock its wavelength to the point of highest sensitivity and linearity of the interferometric fringe for a stable readout. A normalized noise equivalent absorption of 5·10-6 Wcm-1Hz-1/2 was achieved corresponding to 1.4 ppm of NO.

Intra-partum hypoxia is the principal cause of death for every 2 in 10000 infants. Monitoring hypoxia during child-birth will not only prevent infant mortality, but also help prevent cerebral palsy in 10-20% of the surviving babies. Current monitoring techniques either use an indirect biomarker (heart-rate in cardiotocograph) or measure downstream biomarkers intermittently and invasively (fetal blood sampling). For complete fetal wellbeing monitoring, a continuous non-invasive assessment of multiple biomarkers is needed during birth. To address this gap we are developing a noninvasive, continuous sensor based on long wavelength near infrared (LW-NIR) spectroscopic technique for the detection of fetal hypoxia through multiple biomarkers. For specific hypoxia assessment we have identified key optical spectroscopy compatible biomarkers from a list of various biomarkers effected in the physiological processes leading to the development of hypoxia. The key biomarkers identified are – cytochrome-C oxidase, oxygenated and deoxygenated hemoglobin, lactate, pyruvate and pH in the connective tissue in presence of other interferences such as lipids, proteins and other sugars. To translate these biomarkers into a viable diffuse-reflectance probe we assessed the light-tissue interaction in the low-scattering, water-absorption dominated LW-NIR window of 1350-2500 nm using Monte Carlo photon migration model and experimentally verified the penetration depth achievable in fetal tissue phantom to ~0.5 mm, only targeting the capillary bed.

Photothermal Spectroscopy (PTS) is an indirect analytical technique in which the optical signal is directly proportional to the laser emission intensity. This direct dependence on the laser power means that - in contrast to more conventional transmission-absorption techniques - PTS fully benefits from the high power of novel tunable mid-infrared laser sources such as Quantum Cascade Lasers (QCLs). In particular, QCLs equipped with an external cavity (EC) allow broad tunability which can be exploited in the detection of liquids identified by broad absorption bands. To achieve high sensitivity in PTS it is also important to choose a sensitive mode of transducing photothermal signal. Among the PTS transduction techniques photothermal interferometry (i.e. the detection of the phase change resulting from sample heating) stands out due to its high sensitivity. In this work, we use an EC-QCL in a photothermal interferometry PTS setup for trace water detection. We employ a HeNe laser-based Mach-Zehnder Interferometer (MZI) with liquid flow-cells inserted in the two arms. An EC-QCL emitting in the range of 1570-1730 cm^-1 is arranged co-linear to the analyte arm of the interferometer and used to target the bending mode (𝜈₂ ~ 1645 cm^-1) of water molecules in different matrices. Highest linearity and sensitivity are ensured by locking the MZI at its quadrature point via an active-feedback loop. Fluctuations and drifts are further minimized by means of temperature stabilization. When benchmarking the system against commercial FTIR spectrometers it is shown to be in excellent agreement with regards to band shapes, band positions and relative intensities and to compare favorably in terms of sensitivity. Achieved limits of detection (LODs) for water in chloroform and jet-fuel are in the low ppm range. Higher LODs orders of magnitude were obtained indeed for the case of water in ethanol. An analysis of the matrix influence on the PTS signal’s strength has been carried out. Results show how the choice of the matrix dramatically influences limits of detection and limits of quantification (LOQs).

Fiber-optic distributed acoustic sensor (DAS) has been deployed for real-time monitoring of various physical phenomena. The operational principle of DAS relies on monitoring backscattered light from a fiber while leaving the pump optical pulses to get wasted at the fiber distal end. Here, we report on energy harvesting from the DAS pump optical signal to supply energy to passive devices. In this work, a DAS over a ∼1.1-km single-mode fiber (SMF) detects a 200-Hz vibration event produced by a piezoelectric transducer (PZT) while harvesting a 1.58–mW optical signal to charge a 10-F supercapacitor.

Plasma is widely used in etching, deposition, ashing, and ion implantation processes in the manufacturing processes of semiconductor and display devices. Recently, the role of plasma in semiconductor processes is becoming important because the pattern with high step coverage and aspect ratio is required as the semiconductor process is scaled. In particular, plasma-enhanced atomic layer deposition (PE-ALD) is recently highlighted with excellent deposition uniformity compared to chemical vapor deposition (CVD) and physical vapor deposition (PVD) technologies. The density and the state of plasma during the process cannot always remain constant and can be changed by process variables and unpredictable process random fluctuations. Since this can cause yield drop and decrease in productivity, the methodology for monitoring and diagnosing the abnormality of plasma in real time during the process is essentially required. In this paper, the plasma monitoring using the optical emission spectroscopy (OES) in PE-ALD equipment to analyze the characteristics of the process variables. Based on the diagnosis results, the optimal process variable values were proposed, and a process performance predictive model is introduced by analyzing the correlation between variables. Based on the modeling results, the modeling output for the final deposited thickness can be predicted by the initial deposition rate, which can be developed as a virtual metrology system application. In addition, by applying this proposed virtual metrology scheme for the advanced process control (APC), it is possible to estimate the process output without whole wafer measuring, thereby improving the time and cost losses and the wafer-to-wafer variation in the semiconductor manufacturing industry.

Hyperspectral imaging is a key technology for monitoring agricultural crops and vegetation. It can be used for health estimation and the early detection of disease symptoms in plants. This can help to reduce the use of pesticides by allowing targeted and early intervention. Cost-efficient hyperspectral imaging systems are necessary to meet the increasing demand for monitoring techniques for agricultural products. These systems usually suffer from sub-optimal image quality. Here we present a digital aberration correction for hyperspectral image data.

Spectroscopic ellipsometry is a sensitive and optical model-supported quantitative tool to monitor interfaces. In this work, solid-liquid interfaces are studied using the Kretschmann-Raether configuration for biosensing applications. The interface layers support two purposes simultaneously: (i) chemical suitability for the adsorption of molecules to be detected and (ii) the optical enhancement of the signal to increase the sensitivity. Ellipsometry is not only used as a sensor but also as a quantitative measurement tool to study and understand the interface phenomena, and to develop the sensing layers for the largest possible optical sensitivity. Plasmonic and structured layers are of primary importance in terms of optical sensitivity. Layers structured both in lateral and vertical directions have been studied. Optical models based on both the transfer matrix and the finite element method were developed and used for the structural analysis where the material and geometrical derivatives are used in the inverse fitting process of the model data to the measurement. Structures utilizing plasmonic, diffraction, multilayer field enhancement, and other methods were analyzed as possible candidates for the improvement of the optical performance of the cell. Combinatorial and periodic plasmonic surface structures were developed to enhance the sensitivity of in-situ ellipsometry at solid-liquid interfaces utilizing the Kretschmann-Raether (KR) geometry. Ag_xAl_1−x layers with variable compositions and Au layers with changing periods and critical dimensions were investigated to improve the performance of sensors based on the KR arrangement.

In coaxial illumination telecentric imaging optical systems such as microscopes and imaging cameras, functions such as surface shape observation and wide-field confocal observation are realized by placing a spatial polarization control device on the pupil plane of the objective lens. The measurement principle is the detection of changes in polarization distribution between the incident light and the detected light. The slight change in the optical path that occurs with the reflection on the sample surface is converted into polarization information by the spatial polarization control device. Thus, changes in the light path caused by the tilt of the sample surface, scattering due to nano-unevenness, and focus out of the sample are projected as polarization images on the camera.

Wave Front Phase Imaging (WFPI) is a new technique for measuring the free shape of a silicon wafer. To avoid the effects of gravity affecting the wafer shape, the silicon wafer is held vertically while measured using a custom made three-point wafer holder. The wave front phase is measuring using a non-coherent light source that is collimated and then reflected off the silicon wafer surface. The wave front phase is measured using a unique new method that only needs to record the intensity of the reflected light at two or more distances along the optical path. Since only intensity images are used to generate the phase, commercially available CMOS sensors with very high pixel count are used, which enables very high number of data points to be collected at the time required by the cameras shutter speed when using a dual camera setup with simultaneous image acquisition. In the current lab system, a single camera on a linear translation stage is used that acquires 16.3 million data points in 12 seconds, including the stage motion, on a full 300mm wafer providing lateral pixel resolution of 65μm. The flatness of the silicon wafers used to manufacture integrated circuits (IC) is controlled to tight tolerances to help ensure that the full wafer is sufficiently flat for lithographic processing. Advanced lithographic patterning processes require a detailed map of the free, non-gravitational wafer shape, to avoid overlay errors caused by depth-of-focus issues. We present WFPI as a new technique for measuring the free shape of a silicon wafer with high resolution and high data count acquired at very high-speed using a system where the wafer is held vertically without the effects of gravity.

In conjunction with the NASA LaRC SAGE IV Pathfinder team, Quartus has developed a small format neardiffraction limited telescope designed to package into a 6U CubeSat. The SAGE IV Pathfinder telescope utilizes analytical models and designs that can be leveraged to meet a broad range of scientific optical mission needs by creating a family of semi-custom small format space-borne optical systems. During the initial phases of a science mission, a systems engineering assessment can be performed to identify existing designs and analysis tools that can be leveraged to meet many key requirements. This would allow limited resources to then be focused on developing required new components, as opposed to designing the entire optical system from the bottom up. This accelerates technical readiness level (TRL) progression on semi-custom small format precision optical systems, reducing instrument costs, and achieving economy of scale typically not available on one-off science payloads. The current SAGE SBIR Phase II is a research program utilizing a SAGE-like design for development of STOP analysis correlation methodologies. Wavefront error (WFE) is captured over a variety of temperature ranges for comparison to finite element model (FEM) predictions. The accuracy and repeatability of the WFE measurement process over temperature is reviewed. Best practices for accurate STOP analysis and WFE predictions are summarized including modeling parameters, material properties, and strength and distortion assessments.

To meet the requirements for multi-species gas analysis, Quartz-Enhanced Photo-Acoustic Spectroscopy (QEPAS) is used in combination with an IC-based External Cavity Laser system (IC-ECL). The laser system allows the coverage of a wavelength range of 285 nm with an output power of several mW. By integrating piezoelectric actuators as well as resonantly driven MEMS actuators, extremely high sampling rates can be achieved. In this work, results on the detection of multiple trace gases by sequential quasi-simultaneous measurements are presented. The requirements of multi-species detection, output power, tuning range and detection rate are met by our work.

Integrated FMCW LiDARs and their application in Advanced Driver Assistance Systems besides photonic integration involve meeting the vital requirements for accuracy, range detection and object velocity. Automotive LiDARs need to provide a high detection probability and ranging accuracy of moving objects at distances up to hundreds of meters. Precision control of the modulation waveform keeping a high degree of coherency is the pre-requisition for reliable ranging. We have separated the terms of frequency linearization and stabilization, which are responsible for the linearity of the detected response, accuracy, and detection probability of a LiDAR. The required phase-locked loop bandwidth maximum of 500 kHz for the laser control system is specified for a 300-meter measurement range. Requirements for a laser modulation waveform linearity for FMCW LiDAR could be simplified by introducing the scaling factor that is strictly determined by the residual deviation function. Additionally, the practical aspects of laser linewidth and frequency noise density spectrum distribution influence on the detection probability are demonstrated. As a result, optimized criteria for laser swept source performance are proposed, which can be used for the development of long-range detection systems. Finally, the practical results of frequency chirp characterization and ranging performance over 100 meters are demonstrated.

Enantiomeric excess, the ratio between two enantiomers, is an important process variable in chiral catalysis. To increase the efficiency of such processes, this parameter needs to be monitored as close to real time as possible and ideally without elaborate sample preparation. Vibrational circular dichroism (VCD) provides chiral information in a pretreatment free and nondestructive manner. Since classical VCD suffers from a low time resolution, quantum cascade laser (QCL) based VCD was introduced to enable studying more dynamic processes. This significantly improved time resolution enables the use of EC-QCL VCD for monitoring the change of EE e.g. in a chemical process or a chemical reaction. In such applications, the classical approach of human interpretation of individual VCD spectra is no longer reasonable. Hence, chemometric evaluation of VCD spectral datasets is required. In this work we compare accuracy and stability of common multivariate regression algorithms for predicting EE from EC-QCL VCD spectra. Besides classical partial-least-squares regression, modified multiple linear regressions and models derived from chemical knowledge were investigated. We found that a combination of introducing chemical knowledge via spectral descriptor and a reduction of multicollinearity by a ridge regression model resulted in the most stable prediction. Additionally, least absolute shrinkage and selection operator (Lasso) revealed a potential for sensor design involving dedicated QCL arrays focused on a few relevant wavelengths. In summary, a more comprehensive chemometric perspective on QCL-VCD spectra can yield improvements in predictive performance and the shorter measurement times provided by QCL-VCD aid in acquiring datasets of appropriate size.

A range-resolved laser interferometer is the leading candidate for providing displacement metrology that can meet the stringent precision and low power dissipation requirements of cryogenic space astronomy missions. In prior work, a three-phase homodyne laser interferometer was developed using a simple optical and signal processing scheme that achieved the desired dynamic performance required for state-of-the-art cryogenic far-infrared spectrometers, however, the system required three detectors and amplifiers, and exhibited poor performance at low speeds due to 1/f noise associated with the detector and electronics.1,2 A frequency modulation continuous wave (FMCW) heterodyne approach was subsequently adopted to address this shortcoming by shifting the signal of interest well away from the 1/f region.1,3 This technique provides the additional advantage of enabling simultaneous multiaxis measurements all using a single laser and a single detector. This paper discusses several applications of the multiaxis FMCW design that as currently implemented can provide simultaneous measurements of up to 8 axes. The need for a precise and intrinsically low power 1-D displacement metrology system to measure the optical path difference of a cryogenic Fourier transform spectrometer was the initial driver for this research; applications in N-dimensions are currently being explored. Several applications of the technique at both high and low speeds are considered, including multiaxis precision linear positioning, the simultaneous measurement of the cryogenic coefficients of thermal expansion for multiple materials, and cryogenic accelerometry. Results from these applications will be presented and used to discuss limitations of the technique.

Arsenic (As) is recognized as one of the main toxicants worldwide. Arsenic in the environment can be due to natural sources such as the weathering of rocks and volcanic material, but its presence is increasing due to anthropogenic activities such as the use of pesticides, industrial waste and smelting. The accumulation of this heavy metal in the biosphere produces serious effects on the environment and health. Nowadays, the removal of As from drinking water to respect the law limit involves high costs filtering systems. Therefore, a low cost and eco-sustainable strategy based on the use of ferns for phytodepuration of As-contaminated groundwater was developed. The aim of this work was to investigate the possibility of monitoring, by spectroscopy working in the Vis–SWIR regions (350 – 2500 nm), the phytoextraction capacity of the hyper-accumulator Pteris vittata fern, hydroponically grown in greenhouse conditions. The proposed approach is non-destructive, being based on the acquisition of spectroscopic data on fern leaves, followed by chemometric analysis. Reflectance spectra were acquired by a portable spectrophotoradiometer (ASD FieldSpec® 4 Standard–Res). Comparative evaluations were then performed analyzing Pteris vittata leaves (fronds) collected from plants grown on both As contaminated and not contaminated water. The achieved results are very promising for the further development of a full on-site scale monitoring of the phytoremediation process.

The construction sector produces more than one-third of the world’s solid waste. Construction and demolition waste (CDWs) are generated from the construction, renovation and demolition of buildings, roads, bridges and other structures. Moreover, CDW include the materials that may suddenly be generated by natural disasters, such as earthquakes and floods. Post-earthquake building waste (PBW) is typically composed of a mixture of different materials, such as concrete, bricks, tiles, ceramics, wood, glass, gypsum and plastic. These materials represent, if properly separated, a high potential for recycling and reuse particularly the inert fraction, representing about 70% of the total. From this perspective, this work aims to develop an innovative strategy based on optical sensing in order to identify and classify different types of PBW coming from a post-earthquake site (Amatrice, Italy). A strategy based on hyperspectral imaging (HSI) working in the SWIR range (1000-2500 nm) was developed. The acquired hyperspectral images were analyzed using different chemometric methods: principal component analysis (PCA) for data exploration and partial least-square-discriminant analysis (PLSDA) to build a classification model. Results showed that the proposed approach allows to recognize and classify inert fractions from contaminants (i.e., wood, plastics and drywall). The obtained results show how HSI could be particularly suitable to perform classification in complex scenarios as produced by earthquakes.

Astigmatism has a very unique ability to change the shape of the intensity profile of an optical beam as we move away on either side of the focal plane of the optical system. This property of astigmatism can be used to measure the focussing error or the amplitude of defocus present at the plane of measurement. The use of astigmatism to measure focussing error is a very simple and easily implementable process. Astigmatism can be introduced with the help of an astigmatic lens. The approach provides a direct measure of the amplitude of defocus present in an optical beam from the measure of the intensity at the focal plane. In this paper we put forward a theoretical discussion on the above mentioned approach.

The latest generation of fast-gated cameras based on scientific CMOS (sCMOS) sensor technology provide significant enhancement in terms of high acquisition rates and simultaneous high dynamic range compared to CCD, Interline or EMCCD-based gated detectors. Gated intensified sCMOS technology enables the development of novel approaches to fast spectroscopy, for example in the context of micro Laser-Induced Breakdown Spectroscopy (µLIBS) imaging. We present examples of advanced LIBS imaging enabled by this gated sCMOS technology and latest generation of ultrastable kilohertz Q-switch diode lasers. Spatial resolution down to 10 µm is achieved by incorporating an automated translation stage. Timing diagrams and triggering schemes for the translation state and intensified camera are discussed. LIBS images with up to 4K definition (3840x2160 pixels), obtained in less than 3 hours, are presented. Such results show the spatially resolved elemental distributions of Si, Fe, Cu, Al, Mg, Ca and Ag for several geological samples, demonstrating the high throughput potential of such approach and the great reduction of experimental time, while preserving chemical information integrity.

We report the use of non-contact optical interferometric microscopy (OIM) for surface topographic profiling. A Linnik optical configuration is used to create interferograms of an object surface. When the coherence condition between the two beams is met the phase information of the object surface can be extracted to establish its topographic contour image. Using a four-image phase-shifted algorithm with the synchronization of a piezoelectric actuator reference mirror positioning, the present single camera OIM can reconstruct a surface topography with a field of view of 312 μm × 234 μm, axial resolution of 3.31 nm, and lateral resolution of 488 nm, and an estimated maximum topography depth of 270 nm.

Progress in observational system automation is often constrained by the necessity of human involvement in its operation—limiting the potential of fully remote facilities. With observational installations such as those utilizing lidar or guide star assisted telescopes, a particular challenge is in outdoor laser use. Aircraft and clouds often necessitate the cessation of such laser operation, and in the past, these hazards have been best detected by on-site human observers. This paper instead describes how the utilization of computer vision enables hazard detection in a low-cost system, thus allowing for more efficient use of personnel time. The developed software makes use of computer vision functions such as thresholding, frame subtraction, contour detection, and background subtraction to record the presence of aircraft or clouds. This adaptable solution utilizes a live video feed to make rapid judgements on the safety and/or efficacy of an observation system’s use, thus enabling more complete automation of remote facilities. This system has been developed for use alongside peripheral implements that are engaged based on hazard detection statuses. One relevant example would be a laser shutter engaged to prevent unwanted usage when an aircraft is nearby. As the desire and possibility for such installations grows, the application of this kind of aircraft and cloud detection will continue to grow as well. While the software was designed to work in conjunction with laser-based observation systems, its adaptability also lends itself to applications in fields such as meteoritics and meteorology.

The Next Generation Palomar Spectrograph (NGPS) is a high-throughput medium-resolution broadband spectrograph developed for the Hale telescope. It consists of four spectroscopic channels, where ultraviolet channel covers the region [310-436] nm and delivers a resolving power about 4000 with 0.5 arcsec focal plane sampling at the center wavelength 370 nm. The spectrometer operates in the dome under wide temperature range from -10 degrees to 30 degrees, and temperature variation is around 3 degrees per night. One of the goals of NGPS is to achieve excellent image quality and extremely high stability over a wide temperature range. It is indeed a challenge due to limited selection of optical materials in the ultraviolet waveband. This article introduces different camera concept for the ultraviolet channel of NGPS. The Schmidt reflective camera was finally adopted after evaluation of their performance.