This PDF file contains the front matter associated with SPIE Proceedings Volume 9126, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Photoluminescence as a function of time, wavelength and temperature is used to elucidate the relaxation of energy in PbSe as a function of the structural arrangement of the nanocrystals. The contribution of radiation emission, Förster exchange and nonradiative relaxation are accounted in processes from 77 to 300 K and in the wavelength from 1.65 to 1.20 um and in temporal scales from 1 ns to 10 us. Important contribution to the nonradiative relaxation with the mesoscopic arrangement of the nanocrystals and evidence of the Föster exchange independent of temperature and around 25 ns is measured. The general description of relaxation is used as well to correlate with the complex interaction between nanocrystals.

The ability to confine light in small volumes, associated to low background signals, is an important technological achievement for a number of disciplines such as biology or electronics. In fact, decoupling the source position from the sample area allows an unprecedented sensitivity which can be exploited in different systems. The most direct implications are however related to either Surface Enhanced Raman Scattering (SERS) or Tip Enhanced Raman Scattering (TERS). Furthermore, while the combination with super-hydrophobic patterns can overcome the typical diffusion limit of sensors, focused surface plasmons decaying into hot electrons can be exploited to study the electronic properties of the sample by means of a Schottky junction. Within this paper these techniques will be briefly described and the key role played by both surface and localized plasmons will be highlighted.

It has recently been shown possible to directly generate an optical vortex (a beam of light endowed with orbital angular momentum) by spontaneous emission from a molecular exciton array. This contrasts with most established methods, which typically rely on the modification of a conventional beam by an appropriate optical element (for example, a q-plate) to impose the requisite helical twist of a vortex. The new procedure is achieved by nanofabricating a chiral arrangement of chromophores into a ring of specifically configured symmetry, supporting a doubly degenerate (conjugated) exciton with the appropriate azimuthal phase progression. It emerges that the symmetry elements present in the phase structure of the optical field, produced by emission from these degenerate excitons on a array, exhibits precisely the sought character of an optical vortex. The highest order of exciton symmetry, including the corresponding splitting of the electronic states, dictates the maximum magnitude of the topological charge. Work is now progressing on computer simulations aiming to reveal the detailed pattern of polarization behaviour in the emitted light, in which the vector character of the beam progresses around the phase singularity along the beam propagation axis. Significantly, this analysis points to the emission of radiation with polarization varying over the beam profile.

The highly confined nature of the fields from surface plasmons makes them excellent candidates for future nano-optical devices. Most often, optical excitation is used to excite surface plasmons. However, a local, low energy, electrical method for surface plasmon excitation would be preferable for device applications. The scanning tunneling microscope (STM) is an ideal, low energy, local source of electrons that can excite both localized (LSP) and propagating surface plasmons (SPP). Its local nature, along with the ability to precisely position the excitation source and the absence of any background light from the excitation are essential for our experiments. We have used this technique to locally excite surface plasmons on a variety of metal structures. In our setup, the STM is coupled to an inverted optical microscope and the resulting emitted light is collected through the glass substrate. In such a configuration, both the light emitted from localized plasmons as well as the leakage radiation from propagating surface plasmons may be recorded. Both real plane (spatial information) and Fourier plane (angular information) images may be obtained, as well as emission spectra. In this article we will present the results of STM-SPP excitation on thin Au films on glass and investigate the effect of Au film thickness on the SPP propagation length. These results demonstrate the unique features of STM-excited SPPs: the STM plasmon source may be considered equivalent to a series of oscillating vertical point dipoles, and the resulting plasmons consist of a 2D circular wave with a broadband spectrum. These properties are then exploited to study how SPPs scatter into photons from super and sub-wavelength sized holes. It is found that the larger the hole diameter, the more directional the scattering light. From a type of SPP-Young's experiment we determine that the orientation of the electric field is maintained when SPPs are scattered into photons at holes.

For single photon experiments or research on novel hybrid structures consisting of several colloidal quantum dots (Qdots) and plasmonic nanoparticles both the precise localization and the optical behavior of the emitters need to be correlated. Therefore, the gap between the high spatial resolution topography information that provides detailed localization of single Qdots and the diffraction limited fluorescence image needs to be overcome. In this paper, we demonstrate the combination of atomic force microscopy (AFM) with wide-field fluorescence microscopy improved by superresolution optical fluctuation imaging (SOFI). With this approach the topography and the superresolution image can be overlaid with sub-diffraction precision. Consequently, we discriminate between single Qdots that are optically active and dark ones. Additionally, the optical time-dependent behavior of molecular emitters can be selectively investigated. This method is, furthermore, useful for an advanced manipulation and characterization toolbox of Qdots in general. In summary, our findings represent an easily adaptable, highly reproducible and comparatively cheap subdiffraction limit imaging method and they facilitate the efficient selection of bright Qdots in a standard lab environment for proof-of-principle nanostructures containing Qdots and for nanomanipulation experiments.

In this paper we describe the double nanohole laser tweezer system used to trap single nanoparticles. We cover the basic theory behind the DNH and what makes it more powerful than traditional laser tweezers commonly used for larger particles. We outline the basic setup used to reliably trap several different types of particles ranging in size from 1 nm to 40 nm. Data from several experiments is shown which displays exactly how a particle is confirmed to be trapped. We will discuss the use of autocorrelation as well as other information that can be extracted from the optical transmission in our setup and how it has been applied to the identification of protein small molecule interactions and protein binding. Other uses of the data collected from our setup will be discussed including the observation of protein folding. Finally we discuss the current developments of the process and its possible uses as a drug discovery tool, a new type of single particle nanopipette and new bio-sensors.

To understand the forces and dynamics of two or more neutral particles trapped within an optical beam, careful consideration of the influence of inter-particle forces is required. The well-known, field-independent intrinsic force is known to derive from the Casimir-Polder interaction. However, the magnitude of this force may be over-ridden by the effect known as optical binding, in cases when the laser beam is of sufficient intensity. This binding interaction is completely independent of optomechanical effects relating to optical tweezers, and involves a stimulated (pairwise) forward-scattering process. Unlike the Casimir-Polder coupling, optical binding is not always an attractive force when both particles are in their ground state. Associated with optical binding are potential energy surfaces, which reveal intricate patterns of local minima – sets of positions in which one of the particles will sit at equilibrium (with the other notionally set at the origin). These optical energy landscapes, which can be illustrated by use of contour diagrams, have mostly been considered for systems in which spherical particles are optically bound. The effect of different particle shapes, for example tube-like structures, can also be explored. Moreover, although the theory of conventional optical binding generally assumes situations in which both particles reside in their ground states, new results arise when individual particles are excited to a higher electronic state. Although, in the experimentally most convenient structural configuration (for tumbling spherical particles), pairwise optical binding vanishes in the short-range region, novel effects can arise as a result of non-zero optical binding between three neighbouring particles.

An original optical tweezers using two chemically etched fiber nano-tips is presented. Optical trapping of 1 micrometer polystyrene spheres is demonstrated at optical powers down to 2.6 mW and tip-to-tip distances up to 28 µm. Harmonic trap potentials are found by analyzing the trapped particle position fluctuations. The trap stiffness is deduced using three different models. Consistent values of up to 0.5 fN nm_-1 are found. The trap stiffness is linearly decreasing with decreasing light intensity and increasing fiber tip-to-tip distance.

Experimental data on detection and identification of variety of biochemical agents, such as proteins, microelements, antibiotic of different generation etc. in both single and multi component solutions under varied in wide range concentration analyzed on the light scattering parameters of whispering gallery mode optical resonance based sensor are represented. Multiplexing on parameters and components has been realized using developed fluidic sensor cell with fixed in adhesive layer dielectric microspheres and data processing. Biochemical component identification has been performed by developed network analysis techniques. Developed approach is demonstrated to be applicable both for single agent and for multi component biochemical analysis. Novel technique based on optical resonance on microring structures, plasmon resonance and identification tools has been developed. To improve a sensitivity of microring structures microspheres fixed by adhesive had been treated previously by gold nanoparticle solution. Another technique used thin film gold layers deposited on the substrate below adhesive. Both biomolecule and nanoparticle injections caused considerable changes of optical resonance spectra. Plasmonic gold layers under optimized thickness also improve parameters of optical resonance spectra. Biochemical component identification has been also performed by developed network analysis techniques both for single and for multi component solution. So advantages of plasmon enhancing optical microcavity resonance with multiparameter identification tools is used for development of a new platform for ultra sensitive label-free biomedical sensor.

The theory of surface plasmon polariton (SPP) amplification in the metal-insulator-metal structure is developed from first principles. Basing on the dyadic Green’s function of the structure, an exact analytical expression for the gain coefficient is derived. It is shown that the amplification can occur without a population inversion and can reach giant (∼ 10⁶ cm⁻¹) values. The physical origin of this effect is associated with a positive feedback provided by the reflecting waveguide walls that does not require an external pumping. It is also predicted that the same physical phenomenon can lead to SPP generation and the corresponding threshold condition is obtained. It is stressed that such an effect does not imply stimulated emission in the structure and is principally different from SPASER.

Our main goal is to describe the basic steps for the emission control of the electromagnetic field leaving a tailored slit on a gold film, combined with a plasmonic grating designed on the output face, in order to make the emitted beam acquire the desired irradiation diagram (ID). A suitable numerical tool developed for a fast evaluation of the slit-grating system’s ID allows to spare time in the definition of the selected configurations. The customization of the ID is a primary step for the design of more complex structures with potential useful capabilities for the manipulation of impinging light waves and the consequent rise of interesting electromagnetic patterns.

In order to produce the most effective Ag nanoarrays for plasmon enhanced fluorescence and Raman scattering made using ferroelectric substrates, the optimum conditions for the creation of arrays must be identified. We study here Ag nanopattern arrays formed using ferroelectric lithography based on periodically proton exchanged (PPE) template methods. We examine different conditions in regard to deposition of Ag nanoparticles and analyze the plasmon enhanced signal from the resulting nanoarray. We apply FLIM (fluorescence lifetime imaging) to assess different Ag nanoarray preparation conditions on fluorescence emission from selected fluorphores. In addition, we apply Raman and luminescence spectroscopy with AFM (atomic force microscopy) to study the plasmon enhancement of luminescence and Raman from the Ag nanoarrays.

Incorporating resonant optical properties of metal nanostructures into nanoscale applications such as ultrahigh density storage devices, nanoelectronics, and nanophotonics has gained considerable interest within the last years. Recent advances in hybrid and molecular plasmonics are presented. The approach relies on near-field energy transfer between metal nanoparticles and other molecular material, and is not diffraction-limited. We will see that optical nanosources supported by metal nanoparticles can be used for controlling/triggering photochemical and photo physical processes involving photons, charges and motion transfers at the nanoscale. In particular, three examples will be presented and commented: free radical photopolymerization, photo isomerization and nanoscale strong coupling. These examples open new routes including optical near-field photography of ultra confined fields, mode hybridizing in single nanoparticles, molecular optical nanomotors, and new anisotropic nanoemitters.

Although discovered 40 years ago, the interest in surface enhanced Raman spectroscopy (SERS) for a variety of applications in the fields of material and biomaterial has been revived over the past decade mostly due to a better control over the fabrication methods of nanoscale metallic structures. Metallic structures prepared by bottom-up or top-down methods can be tailored for a variety of applications in order to benefit from the best conditions for surface enhancement. SERS platforms made by nanosphere lithography are for example very versatile platforms that show a detection limit in the femtomolar range. Although quantitative measurements are difficult to perform in Raman spectroscopy, the plasmon-mediated enhancement by the metallic nanostructures are of great interest to improve the detection of analytes traces at surfaces. The extension of SERS to tip-enhanced Raman spectroscopy (TERS) is also very valuable to improve spatial resolution of Raman measurements and to yield surface signals, thus making TERS spectroscopy a surface specific technique. Herein we review SERS and TERS measurements of a model molecule (nitrothiophenol) adsorbed onto gold surfaces.

The selective synthesis of gold nanoparticles of any desired size is of great interest. Benzophenone in THF has proved to act as an efficient photocatalyst for the growth of thiolate-capped nanoparticles in the presence and in the absence of gold salts. Consequently, we explored the effect of applying thermal energy to control these processes. These studies have provided key information for the effective growth of gold nanoparticles tailored to specific applications.

The detection and identification of nanoparticles has caught the attention in the last decade due to its potential application on small bio-particles. Raman spectroscopy stands out as a label-free technique for the detection of such particles. However, it may require a high concentration of particles. In a solution with low concentration of particles to detect Raman spectroscopy, the number of particles in the detection area can be increased by optical trapping. The optical trapping force applied to a dielectric nanoparticle is proportional to the gradient of the optical intensity field. Plasmonic nanopores are efficient platforms for trapping nanoparticles due to highly enhanced localized field and its high gradient. Here, we report our work on the optical trapping and assembly of 20 nm polystyrene nanoparticles in a plasmonic nanopore and its detection by Raman spectroscopy.

Interactions between light and molecular matter featuring photon absorption are commonly associated with excitation of individual chromophores. Subsequent relaxation is achieved through numerous mechanisms, such as scattering and energy transfer to neighbouring chromophores. The efficiency of such processes depends on many factors, including the intensity and wavelength of the optical input, the absorption cross-section of the molecule and the relative orientation of molecular components. New photonic materials are developed on the principle that such factors are controllable, duly tailoring the system to suit new technological applications. The parameters that determine the linear response in multicomponent materials are typically assessed within the theoretical framework of classical optics. However, with improved interest and capability in fabricating nanoscale structures (especially those that exhibit quantum effects), it is becoming increasingly relevant to develop theory that more faithfully represents how individual photons engage with matter. In such constructs, the interaction of materials with optical waves and photons is highly dependent on local molecular environment, therefore surrounding structures and ancillary species exert forms of influence on the photophysical processes inherent within dielectric media. At optical wavelengths where the secondary structure displays little intrinsic optical absorption, the role of such components is often interpreted as modifying the input through a corrective local index of refraction. Although expedient in the discussion of bulk properties of a macroscopic medium, it is reasonably supposed at a local chromophore-photon level that optical mechanisms operate in a different fashion. Using a fully quantized approach to the representation of local molecular electronic structure and electrodynamics, this research develops rigorous theory and a corresponding physical interpretation of how photon absorption, scattering and energy transfer are modified by vicinal, non-absorbing chromophores. The results provide insight into the mechanisms achieved within multi-chromophore systems, highlighting factors that assist in the optimization of optical characteristics in designer materials.

Hybrid structures based on CdSe/ZnS quantum dots and porphyrin molecules with effective energy transfer were formed in samples of polymer track pore membrane. It was observed that energy transfer efficiency depends on quantum dot size and correlates with overlapping integral between quantum dot photoluminescence and porphyrin absorption spectra inherent for Förster Resonant Energy Transfer, FRET. However, a noticeable deviation of experimental FRET efficiency dependence on an acceptor concentration from theoretical ones was observed for all donor-acceptor pairs. A gradient of donor and acceptor concentrations in the matrix is considered as the most probable reason of this deviation. A theoretical model describing energy transfer in a rigid solution with a gradient of particle concentration is proposed.

Spectroscopically resolved emission from single nanocrystals at cryogenic temperatures provides unique insight into photophysical processes that occur within these materials. At low temperatures the emission spectra collapse to narrow lines revealing a rich spectroscopic landscape and unexpected properties, completely hidden at the ensemble level. Since these techniques were first used, the technology of nanocrystal synthesis has matured significantly and new materials with outstanding photophysical stability have been reported. Here we review our recent work that shows how cryogenic spectroscopy of single nanocrystals probes the fundamental excitonic structure of the band edge, revealing spectral fingerprints that are highly sensitive to a range of photophysical properties as well as nanocrystal morphology. In particular, spectral and temporal signatures of biexciton and trion emission are revealed and their relevance to emerging technologies discussed. In addition, we show how high resolution excitation spectroscopy can provide information on external processes that ultimately limit the coherence of the nanocrystal band-edge states. Overall we demonstrate how cryogenic single nanocrystal spectroscopy can be used as a vital tool for understanding fundamental photophysics and guiding the synthesis of new nanocrystal materials.

Recently, the use of stereospecific chiral stabilising molecules has also opened another avenue of interest in the area of quantum dot (QD) research. The main goal of our research is to develop new types of technologically important quantum dot materials containing chiral defects, study their properties and explore their applications. The utilisation of chiral penicillamine stabilisers allowed the preparation of new water soluble white emitting CdS quantum nanostructures which demonstrated circular dichroism in the band-edge region of the spectrum. It was also demonstrated that all three types of QDs (D-, L-, and Rac penicillamine stabilised) show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. In this work the chiral CdS based quantum nanostructures have also been doped by copper metal ions and new chiral penicilamine stabilized CuS nanoparticles have been prepared and investigated. It was found that copper doping had a strong effect at low levels in the synthesis of chiral CdS nanostructures. We expect that this research will open new horizons in the chemistry of chiral nanomaterials and their application in biotechnology, sensing and asymmetric synthesis.

We present a theoretical scheme for laser cooling of the colloidal cadmium selenide (CbSe) QDs. The laser cooling process is based on the anti-Stokes fluorescence observed in QDs. We have considered laser cooling in the system of identical CdSe QDs laser pumped with energy of photons less than mean fluorescence energy. The dependences of all parameters of the system on the temperature have been taken into account. Following to our simulation the laser cooling with temperature drop ~100K can be realised with well technologically developed today passivated CdSe QDs.

We present an iterative design method for the coupling and the mode conversion of arbitrary modes to focused surface plasmons using a large array of aperiodically randomly located slits in a thin metal lm. As the distance between the slits is small and the number of slits is large, significant mutual coupling occurs between the slits which makes an accurate computation of the field scattered by the slits difficult. We use an accurate modal source radiator model to efficiently compute the fields in a significantly shorter time compared with three-dimensional (3D) full-field rigorous simulations, so that iterative optimization is efficiently achieved. Since our model accounts for mutual coupling between the slits, the scattering by the slits of both the source wave and the focused surface plasmon can be incorporated in the optimization scheme. We apply this method to the design of various types of couplers for arbitrary fiber modes and a mode demultiplexer that focuses three orthogonal fiber modes to three different foci. Finally, we validate our design results using fully vectorial 3D nite-difference time-domain (FDTD) simulations.

We imaged polarization rotation of transmitted light in 1D Periodic Plasmonic Structures (PPS) fabricated on thin metal coated dielectric substrate. Several PPS of 50% duty cycle and extremely low aspect ratio (height to width ratio) of 0.1 were designed using rigorous coupled wave analysis to exhibit transmission plasmonic resonances at optical wavelengths (400 nm to 700 nm). PPS were fabricated using electron beam lithography, evaporation and lift-off process on glass substrates coated with thin metal. The PPS were characterized using normally incident broadband visible light and crossaxis Polarizer Analyzer setup, with the transmitted light imaged in direct and momentum space using a camera. When the cross axis Polarizer Analyzer were positioned at +45° & -45° respectively w.r.t. plane of incidence, bright emissions of Green, Yellow or Red colors corresponding to transmission plasmonic resonances of the PPS with different periods, were observed in both direct and Fourier planes, instead of completely dark images. From the measured emission momentum in Fourier plane images and spectra of collected light, the emissions were attributed to the excitations of surface plasmons and the reason for surface plasmon excitation in this arrangement is strong coupling of hybrid modes with each other caused by the anisotropy introduced by grating which strongly enhances the efficiency of Polarization rotation. The presented structures behave as frequency selective half wave plates in transmission configuration and could also be used to eliminate the effect of direct beam while imaging the coupling to surface plasmons in periodic structures.

GaN-based light-emitting diode (LED) was successfully fabricated using surface plasmons (SPs) excited at the metal/semiconductor interface. Normally, SPs excited by the interaction between light and metal surfaces were known to enhance the internal quantum efficiency of LEDs via the quantum-wells (QWs) and SPs coupling. The penetration depth of SPs fringing field for the Ag film was calculated as 42.0 nm at an emission wavelength of 460 nm. Thus, the distance between the QWs and metal was critical for QWs-SP coupling. However, the p-GaN layer in blue emissive GaN-based LEDs, which is a sandwich layer between the active and p-type conducting layers, must has a thickness of over 120 nm to ensure the sufficient mobility of carriers. In this study, an Ag nanoparticle layer was coated on p-GaN top layer as the grating structure. The light extraction efficiency of lateral conducting blue LED is expected to be enhanced by the surface plasmon-TM light mode coupling during the localized surface plasmon resonance. Compared to the optoelectronic performance of the conventional LED, the SP-enhanced LED shows the superior performance, even though the silver nanoparticles were placed at least 200 nm away from the quantum-well active layer. The output power of the SP-enhanced LED exhibited over 1.1 times in magnitude as compared with that of the conventional LED at 350 mA, while still keeping nearly the same current-voltage characteristic.

We investigate the dynamics of strongly coupled surface plasmon polaritons (SPP) and molecular excitations (ME) of Sulforhodamine 101 dye. The SPPs are excited by prism coupling technique on a thin silver film with dye molecules embedded in a polymer layer on top of it. Rabi splittings with energies of 135 and 97 meV are observed in the recorded dispersion relations. Both coupled oscillator model and transfer matrix method are used to fit the experimental results. In addition to the common reflectance measurements, polarization resolved detection of scattered signal from the molecular side is also utilized. Simultaneous detection of the scattered polaritons and molecular fluorescence reveals the coexistence of the hybrid modes and pure ME. Dependency of the fluorescence on the excited modes suggests that the hybrid polariton modes decay via dephasing and internal relaxation of the molecules.

Single nanoparticles made of noble metals are strongly appealing to develop practical applications to detect fluorescent molecules in solution. Here, we detail the use of a single gold nanoparticle of 100 nm diameter to enhance the detection of single Alex Fluor 647 fluorescent molecules at high concentrations of several micromolar. We discuss the implementation of fluorescence correlation spectroscopy, and provide a new method to reliably extract the enhanced fluorescence signal stemming from the nanoparticle near-field from the background generated in the confocal volume. The applicability of our method is checked by reporting the invariance of the single molecule results as function of the molecular concentration, and the experimental data is found in good agreement with numerical simulations.

In the investigation of the sensing performance based on localized surface plasmon resonance (LSPR), the bulk sensitivity, which is the spectral shift per refractive index unit upon the change of the surrounding index to spatial infinite, is often measured and considered as the indication of the sensing ability. To the contrary, in biosensing applications only the refractive index in a confined region close to the metal nanostructure surface is altered due to the attachment of the recognition and target molecules. The correlation between the bulk and surface sensitivity is nevertheless ambiguous, especially in strongly coupled plasmonic systems, and rarely discussed in the literature. In this paper, we examine the bulk and surface sensing performance of periodic Au nanodisk arrays on quartz substrates. By means of diffractive coupling of LSPR in the periodic arrays, the bulk sensitivity and the figure of merit (FoM, as high as ~30) could be varied by engineering the coupling strength and adjusting the size of the Au nanodisk and the array pitch. The surface sensing performance is also explored by sequential atomic layer deposition of Al2O3, and the electric field decay from the Au nanodisk surface could thus be extracted using an exponential function. It is demonstrated that in these substrates the surface and bulk sensitivity have an opposite dependence on the coupling strength. In spite of the high bulk sensitivity and FoM in systems with strong coupling, a low surface sensitivity is demonstrated due to the large electric field decay length. Therefore, detailed and careful design of the coupling strength and the surface electric field to match the size of the target biomolecule is very critical for the best sensing performance. Moreover, we provide a more reliable biosensor design protocol based on the surface sensing performance.

The dispersion equation for surface plasmon-polariton (SPP) waves excited in a composite structure obtained by depositing a columnar thin film (CTF) on a metal (silver) substrate decorated periodically by an array of rectangular grooves was analyzed using rigorous coupled-wave approach. Only one solution of this dispersion equation is possible. The characteristics of the SPP wave are affected by the vapor incidence angle chosen to deposit the CTF.

Mg doped ZnO thin films were prepared by magnetron sputtering and were irradiated by linearly polarized femtosecond laser pulse. Scanning electron microscopy (SEM) characterizations illustrated that regularly arranged nanoripples appeared on the ablation area with the period perpendicular to the polarization direction in the range of 250 nm~570 nm, but parallel to the polarization direction in the range of 2.2 µm~2.5 µm. The redshift of Raman peaks was observed at the central ablation area of the nanoripples, while, both blueshift and redshift were found at the edge area, which could be ascribed to the defects as well as the nanoripple structure.

Silicon hybrid photonics has attracted in the last years a growing interest for the integration of various materials within silicon photonics. In this picture, hollow-core slot photonic crystal waveguides play an important role as they allow an efficient overlap between the high electromagnetic power density of propagating modes and the introduced materials. Besides this potential advantage, part of the cost to pay is that light coupling into such waveguides from strip waveguides becomes difficult. We propose here a strategy in order to efficiently side-couple light into such slow light modes, leading to a typical 80% efficiency at nG=30.

In this paper, we report a novel approach for efficient fabrication of mesoscale polymer 3D microstructures. It is implemented by direct laser writing varying exposure beam focusing conditions. By carefully optimizing the fabrication parameters (laser intensity, scanning velocity/exposure time, changing objective lens) complex 3D geometries of the microstructures can be obtained rapidly. Additionally, we demonstrate this without the use of the photoinitiator as photosensitizer doped in the pre-polymer material (SZ2080). At femtosecond pulsed irradiation ~TW/cm² intensities the localized free radical polymerization is achieved via avalanche induced bond braking. Such microstructures have unique biocompatibility and optical transparency as well as optical damage threshold value. By creating the bulk part of the structure using low-NA (0.45) objective and subsequently fabricating the fine features using oil immersion high-NA (1.4) objective the manufacturing time is reduced dramatically (30x is demonstrated). Using this two objective method a prototype of functional microdevice was produced: 80 and 85 µm diameter microfluidic tubes with the fine filter consisting of 4 µm period grating structure that has 400 nm wide threads, which corresponds to a feature precision aspect ratio of ~200. Therefore, such method has great potential as a polymer fabrication tool for mesoscale optical, photonic and biomedical applications as well as highly integrated 3D µ-systems. Furthermore, the proposed approach is not limited to lithography and can be implemented in a more general type of laser writing, such as inscription within transparent materials or substractive manufacturing by ablation.

Chalcogenide glasses are amorphous semiconductors with a number of interesting properties required for photonic devices. Particularly, their optical properties can be tuned through the change of the glass composition. We investigate second-order nonlinear optical properties of chalcogenide glass (Ge27Se64Sb9) thin films fabricated by thermal evaporation. The strong second-harmonic generation observed for the samples investigated is analyzed as a function of incident polarization. Furthermore, the role of multipole effects in second-harmonic generation is also studied by using two beams at the fundamental frequency. Our results suggest that the higher-multipole effects are present and contribute significantly to the second-harmonic response of chalcogenide the samples.

We investigate quantum dots (QDs) of ternary compounds Cd_XHg_1-XSe with 0<X<1 using a Raman scattering technique at room temperature. We obtained the correlation between QDs chemical composition and the frequencies of CdSe-like LO and the HgSe-like TO and LO modes. It is shown that the crystalline structure of original CdSe QDs used for Cd/Hg substitution, either zinc blende or wurtzite affects strongly on structural properties of resultant Cd_XHg_1-XSequantum dots.

X-ray structural analysis is used for investigation of structures, obtained by self-organization from nanoparticles - lead sulfide (PbS) quantum dots (QDs) of different sizes - deposited on a glass substrate or embedded in a porous matrix. These nanostructures obtained by both methods represent ordered close-packed structures of the nanoparticles. The configuration of obtained structures does not depend on the nanoparticle size and type of substrate and matrix.

Concentration-dependent optical properties of lead sulfide (PbS) quantum dots (QDs) embedded into a porous matrix are investigated. A red shift of luminescence peak position depends on QD concentration and evidences for F¨orster resonant energy transfer (FRET) inside the quasi-monodispersed assemblies. PL decay curves show significant influence of FRET process on QD optical properties. PL lifetime size-dependencies are found to be dependent on the QD concentration. The growing impact of FRET process with increasing QD concentration leads to transformation of anomalous size-dependence of PL lifetimes to the inverse. FRET efficiency gradually increases with QD concentration and saturates at 35% that corresponds to the formation of an ordered QD superstructure. Formation of PbS QD superstructure is confirmed by X-ray analysis, while calculated interdot distance in the superstructure coincides with the one obtained by FRET technique.

Erbium-doped Polymer hybrid slot waveguide amplifier at λ_s=1530 nm with a 1480 nm pumping wavelength is investigated. Both, the waveguide structure parameters and the Er³⁺-doped polymer intrinsic spectroscopic parameters are swept to analyze the gain contribution sensitivities. Assuming moderate optical transmission losses of 10dB/cm, the predicted net gain typically varies from 0 to 10dB. Due to the excited state absorption (ESA) mechanism in the high intensity slot region, the signal gain is significantly suppressed for large pumping power, leading to the counterintuitive result that there is an optimum pump power value in the sub-100 mW range. The effect of the ion concentration and the ion-ion interaction is considered giving different adjusted parameters in every particular case.

We present a direct patterning method of dielectric materials via temporally shaped femtosecond laser pulses. A thinfilm waveguide with a 2D periodic pattern of photonic crystals with circular base elements is investigated. We use dielectrics since they are transparent especially in the visible spectral range, but also in UV and near infrared range. Thus, they are very suitable as optical filters in the very same spectral region. Since structuring of non-conductive dielectric materials suffers from charging, the implementation of laser processing as patterning method instead of conventional processing techniques like electron beam lithography or focused ion beams is a very attractive alternative. Despite a low refractive index contrast, we show by numerical results that normal incident of light to the plane of periodicity couples to a waveguide mode and can excite Fano resonances. That makes the device extremely interesting as narrow-band optical filter. Applications of optical filters in the visible and UV range require fabrication of photonic crystal structures in the sub-100 nm range. Temporally shaped femtosecond laser pulses are applied as a novel method for very high precision laser processing of wide band gap materials to create photonic crystal structures in dielectrics. Shaping temporally asymmetric pulse trains enable the production of structures well below the diffraction limit.¹ We combine this process with deposition of a high refractive index layer to achieve the targeted resonant waveguide structure. Additionally, we focus on the rim formation arising by laser processing since this is an important issue for fabrication of photonic crystal arrays with small lattice constants.

We develop a theory of time-resolved pump–probe optical spectroscopy for modelling interband absorption by an anisotropic semiconductor nanodumbbell. By considering three transition schemes where the pump and probe pulses are nearly resonant to a dipole-allowed interband transition of different elements of the nanodumbbell, and assuming that the populations of the exited states are coupled through the nonradiative relaxation processes, we analytically calculate the absorption efficiency of the probe as a function of its delay from the pump for relatively short pulses. The obtained functional dependency, being the sum of exponentials with exponents proportional to the energy relaxation rates of the excited electronic states, is useful for the analysis of experimental absorption spectra aiming at retrieving the relaxation parameters of the nanodumbbell’s electronic subsystem.

We report a giant enhancement of Spin Hall (SH) shift even for normal incidence in an exotic optical system, an inhomogeneous anisotropic medium having complex spatially varying birefringent structure. The spatial variation of birefringence is obtained by changing the three dimensional orientation of liquid crystal by modulating the pixels with user-controlled greyscale value. This polarization dependent spatial variation (in a plane transverse to the direction of propagation of light) of the transmitted light beam (for incident fundamental Gaussian beam lacking any intrinsic angular momentum) through such inhomogeneous anisotropic medium was recorded using an Eigenvalue calibrated Stokes- Mueller imaging system. Giant SH shift was manifested as distinctly different spatial distribution of the recorded output Stokes vector elements for two orthogonal (left and right) input circular polarization states. We unravel the reason for such large enhancement of SH shift by performing rigorous three dimensional analysis of polarization evolution in such complex anisotropic medium. The theoretical analysis revealed that generation of large magnitude of transverse energy flow (quantified via the Poynting vector evolution inside the medium) originating from Spin Orbit Interaction (SOI) in the inhomogeneous birefringent medium leads to the observation of such a large spin dependent deflection of the trajectory of light beam.

Materials with one-dimensional quantum structures are promising for their application in solar cells. The photo-voltage generation of these structures is caused by spatial separation of electron-hole pairs by a built-in electric field in the GaAs p-i-n junction. The InGaAs/GaAs sample shows a significantly higher photo-voltage in the spectral range of 1.25-1.37 eV, as compared to a reference GaAs p-n junction, due to interband transitions in the quantum wires (QWRs).

In this paper we probe the surface enhanced fluorescence (SEF) and Raman scattering (SERS) from arrays of selfstanding Au nanorod arrays embedded within a porous alumina template (AAO). By controlling the thickness of the AAO matrix both SEF and SERS are observed exhibiting an inverse relationship. SERS and SEF show a nonlinear response to the removal of AAO matrix due to an inhomogeneous plasmon activity across the nanorod. Optimization of the level of alumina matrix thickness optimizes conditions for obtaining either maximized SERS, SEF or for simultaneously observing both SERS and SEF together.

We investigate electrical photoresponse of multilayer graphene decorated with CdSe/ZnS quantum dots. It was found that photoresponse of these hybrid structures depends on quantum dot photoluminescence quantum yield. We demonstrate in uence of external factors (light exposure and treatment with ammonia vapors) on photoluminescence quantum yield of quantum dots and electrical photoresponse of the hybrid structures.

An appearance of the photoluminescence anisotropy induced by photochemical reaction under continuous irradiation with polarized light is demonstrated for an ensemble of CdSe/ZnS quantum rods chaotically embedded in the pores of filter paper. A specific relaxation of the photoinduced anisotropy is revealed in darkness after an extended period of irradiation. This process is attributed to rotational diffusion of nanocrystals in the pores of filter paper. The suggested theoretical model is used to estimate the rotational diffusion constant D, which is calculated to be 9.7 × 10^-3 sec^-1 for the sample after 5 hrs of irradiation.

We present technique of obtaining complex hybrid structures combining the multi-walled carbon nanotubes or multi-layer graphene and luminescent hydrophobic semiconductor core/shell quantum dots CdSe/ZnS. As a result, a formation of quantum dot decorated carbon nanotubes and graphene films is evidenced by 2D microluminescence and micro-Raman mapping of quantum dots and nanocarbons, respectively, where a spatial correlation between the luminescence and Raman signals is found.

In this paper, an ormocomp polymer nanowire with possible use in integrated-optics sensing applications is presented. We discuss the structure design, the fabrication process and present results of the simulation and characterization of the optical field profile. Since the nanowires are designed and intended to be used as integrated optics devices, they are attached to tapered and feed waveguides at their ends. The fabrication process in this work is based mainly on the nanoimprint technique. The method assumes a silicon nanowire as an original pattern, and polydimethylsiloxane (PDMS) as thesoft mold. The PDMS mold is directly imprinted on the ormocomp layer and then cured by UV light to form the polymer based nanowire. The ormocomp nanowires are fabricated to have various dimensions of width and length at a fixed 500nm thickness. The length of the nanowires is varied from 250 µm to 2 mm, whereas the width of the structures is varied between 500nm and 1µm. The possible optical mode field profile that occurs in the proposed polymer nanowire design is studied using the H-field finite element method (FEM). In the characterization part, the optical field profile and the intensity at the device output are the main focus of this paper. The various lengths of the nanowires show different characteristics in term of output intensity. An image processing is used to process the image to obtain the intensity of the output signal. A comparison of the optical field and output intensity for each polymer nanowire is also discussed.

Leakage radiation spectroscopy of organic para-Hexaphenylene (p-6P) molecules has been performed in the spectral range 420-675 nm which overlaps with the p-6P photoluminescence band. The p-6P was deposited on 40 nm silver (Ag) films on BK7 glass, covered with SiO2 layers. The SiO2 layer thickness was varied in the range 5-30 nm. Domains of mutually parallelly oriented organic nanofibers were initially grown under high-vacuum conditions by molecular beam epitaxy onto a cleaved muscovite mica substrate and afterwards transferred onto the sample by a soft transfer technique. The sample placed on a flat side of a hemisphere fused silica prism with an index matching liquid was illuminated under normal incidence by a He-Cd 325 nm laser. Two orthogonal linear polarizations were used both parallel and perpendicular to the detection plane. Spectrally resolved leakage radiation was observed on the opposite side of the Ag film (i.e. at the hemisphere prism) as a function of the scattering angle. Each spectrum contains a distinct peak at a wavelength dependent angle above the critical angle. This way the dispersion curve was measured, originating from a hybrid mode, i.e. the interaction between the p-6P excitons and surface plasmon polaritons (SPPs) of the metal/dielectric boundary. The presence of the SiO2 layer considerably changes the dispersion curve in comparison to the one of the Ag/p-6P/air system. However, the Ag/SiO2/p-6P/air stack forms a stable structure allowing construction of organic plasmonic devices such as nano-lasers.

The goal of our paper was to investigate the impact of the necking phenomenon on the optical properties of two gold nanoparticles characterized by a large value of the imaginary part of the refractive index m. Our results show that the difference between various neck types is small, therefore, for the modeling process, we recommend the most simple one, i.e. the cylindrical connector. When a connection between two primary particles is caused by the overlap factor C_ov, and not by the neck size parameter Y_con, the results can be much more erroneous and the possible error should be at least taken into consideration. The position of the extinction peak in a function of the connection size C_ov is dependent on the value of the complex refractive index m. Additionally, the applicability of the DDA (Discrete Dipole Approximation) method for measuring the extinction cross section C_ext of gold structures was studied.

The versatility of ultrashort laser pulses as a tool for laser materials processing has augmented particular interest in the past decade. Especially birefringent modifications, so-called nanogratings, have found to exhibit tremendous potential for manifold photonic functionalities. These self-assembling structures, orienting always perpendicular to the laser polarization, have been up to now extensively studied in bulk fused silica. Commonly it is assumed that the formation of nanogratings is actually limited to anomalous glasses like silica or slightly doped silica. However, we recently found that even in glasses like borosilicate or BK7 nanogratings can be observed within certain parameter regimes. Here we present an extensive study of the fundamental constituents of nanogratings in bulk borosilicate glass using small angle X-ray scattering (SAXS) in combination with focused ion beam milling (FIB) and scanning electron microscopy (SEM). The irradiation produces void-like sheets (10-20 nm wide) as well as elongated cracks of up to 400 nm. In contrast to nanogratings in fused silica, borosilicate shows a significant smaller optical retardance. The cumulative action of several hundreds of laser pulses lead to the formation of individual grating planes with a period of about 60 nm (at an inscribing laser wavelength of 800 nm) while the well-known λ/2n (n-refractive index) period is prevented. This has never been observed for ultrashort pulse induced nanogratings so far.

Plasmonic metal-insulator-metal resonators can be designed to totally absorb an incident light. A combination of such antennas within a sub-wavelength period allows a sorting of the absorbed photons as a function of their wavelength. These structures also exhibit a high electric field enhancement in tiny volumes. We show that this enhancement can be even stronger when the resonator are illuminated with a focused light.

The design of metasurfaces able to efficiently control the polarization state of an electromagnetic wave is of importance for various applications. We demonstrate both theoretically and experimentally that plasmonic planar L-shaped antennas can induce a 90◦-rotation of the linear polarization of light with a nearly total efficiency in the infrared (3-5 µm). The nanoantenna geometry is engineered so that the polarization conversion occurs over a 1 μm-wide spectral band ([3.25-4.25] µm ) with a mean polarization conversion efficiency of 95 %. In order to validate a theoretical model describing the antenna behaviour, we investigate the polarization conversion effect as function of the incident and azimuthal angles.

We report photonic concepts related to injection and sub-wavelength propagation in nanofibers (nanowires and nanotubes). These nanostructures are fabricated by the wetting template method leading to aspect ratio of over 250. At first, injection into nanowires and nanotubes of SU8, a photoresist used for integrated photonics, was successfully achieved by using polymer microlensed fibers with sub-micronic radius of curvature. Theoret- ical simulation by finite domain time-dependent (FDTD) method was used to determine the sub-wavelength propagation for nanowires and nanotubes and corroborate this coupling phenomena. The original confinement of energy density into SU8 nanotubes is highlighted. Finally, characterisation of propagation losses is reported by using a cut-back method transposed to such nanotubes and determined to range between 1 and 2 dB/mm. Both injection and cut-back method developed here are compatible with any sub-micronic structures. This work on SU8 nanofibers suggests broader perspectives for future nanophotonics.

In present study complexes between non-toxic ZnSe/ZnS quantum dots and chlorin e6 molecules that are widely used as photosensitizers in photodynamic therapy were formed. It was found that in aqueous solution cationic ZnSe/ZnS quantum dots and chlorin e6 formed stable complexes that exhibit efficient photoexcitation energy transfer from quantum dots to molecules. Spectroscopic methods were applied to evaluate the energy transfer efficiency. Stoichiometry of these complexes was studied. Additionally, the photodynamic therapy efficacy of the quantum dotchlorin e6 complexes was in vitro assessed against Ehrlich ascites carcinoma cancer cell line using a trypan blue assay. We found that complex offered an improved cancer cell photodynamic destruction effect as compared to that of free chlorin e6.

In this work, we study the behavioral regularity of fullerene C₂₀ inside the icosahedral outer shell of fullerene C₂₄₀. The feature of such two-shell fullerenes is that the internal fullerene will move at low temperatures in a certain way: between the potential wells. The aim of this work is to reveal the regularities for motion of small fullerenes in nanospace of large external icosahedral fullerene, including the identification of the spatial configuration for a multi-well potential of interaction between two objects and prediction of possible movement for the internal object between potential wells. For the fullerene C₂₀ it was found twenty potential wells in the direction of the fifth order axes for icosahedron of fullerene C₂₄₀ cage, thirty towards in the direction of the middle of the ribs and twenty potential wells towards centers of the faces of the icosahedron. The prediction of possible moving for the internal object between potential wells and the regularities of this movement were made based on the relief analysis of the interaction energy surface of fullerenes. The numerical simulation of C₂₀ motion in the field of C₂₄₀ was carried out to test the prediction of movement. As results of the experiment, it was found that the fullerene C₂₀ is easy to jump between the potential wells even at low temperatures up to 300K. Molecular dynamics simulations confirmed our conclusions about regularities of C₂₀ movement between potential wells. Thus, one can conclude that the analysis of the topology of the energy surface of van der Waals interaction between the components of nanoparticles gives a true predictive picture of the regularities of the internal molecule behavior. Probably, the phenomenon of fullerene C₂₀ movement in a cell of another fullerene can be used in modern technologies, such as determining a local temperature by increase of jumping velocity.

(TFBG) covered by silver nanowires aligned perpendicularly to the fiber axis. TBFGs are a convenient way to measure surrounding refractive index, as they provide intrinsic temperature-insensitivity and preserve the optical fiber structural integrity. With bare TFBGs, sensitivity is about 60 nm/RIU (refractive index unit) while when coated with a gold thin film, surface plasmon resonance can be excited leading to a sensitivity about 600 nm/RIU. In our case, we show that localized plasmon resonances can be excited on silver nanowires. These nanowires (100 nm diameter and about 2.5 µm length) were synthetized by polyol process (ethylene glycol reducing silver nitrate in the presence of poly (vinyl pyrrolidone and sodium chloride). The nanowires were aligned and deposited perpendicularly to the fiber axis on the gratings using the Langmuir-Blodgett technique in order to maximise the coupling between azimuthally polarized light modes and the localized plasmons. Excitation of surface plasmons at wavelengths around 1.5 µm occurred, leading to a dip in the polarization dependent losses of the grating. This dip is highly dependent of the surrounding refractive index, leading to a sensitivity of 650 nm/RIU, which is a 10-fold increase compared to bare gratings. We obtain results equal or slightly higher than those obtained using a gold layer on TFBGs. In spite of the comparable bulk refractometric sensitivity, the use of these oriented nanowire layers provide significantly higher contact surface area for biochemical analysis using bioreceptors, and benefit from stronger polarization selectivity between azimuthal and radially polarized modes.

Germanium (Ge) nanoclusters are grown by a molecular-beam epitaxy technique on chemically oxidized Si(100) surface at 700ºC. Evidence for long-term photoinduced changes of surface conductivity in structures with Ge nanoclusters (NCs) grown on silicon oxide is presented. Photoexcitation NCs or Si by quanta with different energy allows observing two non-equilibrium steady-states with excess and shortage of conductivity values as compare to equilibrium one. The persistent photoconductivity (PPC) behaviour was observed after interband excitation of electron-hole pairs in Si(001) substrate. This effect may be attributed to spatial carrier separation of photoexcited electron-hole pairs by macroscopic fields in the depletion layer of near-surface Si. Photoquenching of surface conductivity, driven by optical recharging of Ge NC’s and Si/SiO2 interface states, is observed. Conductivity decay is discussed in the terms of hole`s accumulation by Ge-NC states enhancing the local-potential variations and, therefore, decreasing the surface conductivity of p-Si.

In this study microscopic gas bubbles (7-12 μm diameter) suspended in water were optically trapped in a custom-built microfluidic slide using holographically generated Laguerre-Gaussian (‘doughnut’) beam optical tweezers. The optical potential was then characterized as a function of bubble size, trapping laser power and trapping beam diameter (Laguerre-Gaussian beam mode) using the trap spring constant in the plane transverse to the beam propagation direction, obtained from the position fluctuations of the bubble in the trap measured by video microscopy and particle tracking. It was found that microbubbles were held at the equilibrium position of buoyant and optical forces at a distance from the focus of the beam that increased with laser power, and that optical trapping in this configuration was only possible within a specific range of trap and bubble parameters. Furthermore an optimum size of the doughnut beam to microbubble diameter which maximized the transverse spring constant was found . A ray optics model of the optical forces acting on microbubbles in a focused Laguerre-Gaussian beam was used in order to calculate the trap spring constants and equilibrium trapping position as a function of the different parameters, and highlight key physical behaviours.

A sharp resonance, narrow bandwidth plasmonic cascaded nanofilter is proposed. The resonator is based on Metal- Insulator-Metal (MIM) plasmonic waveguide which has the ability to confine light at sub-wavelength scale. The proposed inline resonator features low loss, compact size, and good sensing characteristics which opens the door for many nanophotonic applications. This structure can be used in many applications such as sensing, biomedical diagnostics and on-chip optical interconnects. For example, it can be used as a highly effective integrated sensor with sensitivity up to 3000 nm RIU^-1.

Changes of optical properties of the solutions of CdSe/ZnS quantum dots (QDs) covered with the trioctylphosphine oxide (TOPO) ligands under the pulsed ultraviolet (UV) laser irradiation are observed. The fluorescence quantum yield (QY) of QDs decreases by more than an order of magnitude when the radiation dose approaches 2 × 10^-15 J per particle. This process is accompanied by a blue shift of both fluorescence and the first excitonic absorption peaks. The fluorescence quenching becomes less pronounced when the overall TOPO content in the solution is increased. When ТОРО ligands are replaced with n-hexadecylamine (HDA), QY and spectral properties are not changed at the same irradiation conditions. We assume that the above changes of the optical properties are associated with photooxidation of TOPO ligands by excited QD. Such process is less probable for the HDA ligand due to its different energy structure.

It is known that manufacturing and applications of photonic crystals is currently an area of much interest. One of the focuses of special attention in this area is various microcavity (MC) devices. Porous silicon is one of the most promising materials for manufacturing such devices because it is simple to prepare, its optical parameters are precisely controllable, and it has an enormous surface area. This allows to inject different kinds of luminophores into porous silicon MC devices. Apparently, semiconductor quantum dots (QDs) are among the most interesting of them. QDs are characterized by a wide absorbance spectrum, large absorption cross-section, high quantum yield, and excellent photostability. To date, there have been few studies on QD injection into porous silicon photonic structures. In addition, many structures used lack the desired characteristics; the depth of QD penetration also remains a question. This is the first study to analyze the photoluminescence spectrum and kinetics of QDs in a high-quality porous silicon MC. A drastic narrowing of the luminescence spectrum has been observed after QD injection. We have found that the MC morphology considerably affects the penetration of QDs. The kinetics of photoluminescence has also been investigated. Measurements have shown a decrease in the QD characteristic photoluminescence decay time after QD injection into a porous silicon MC compared with the QD photoluminescence decay time in a toluene solution. However, we have not observed a significant difference between the photoluminescence decay times of QDs in an MC and in single-layer porous silicon.

It has been well documented that ideal SERS conditions occur in the nano sized gaps between metal nanoparticles ^1,2 . Aggregation of the nanoparticles is a very simple and effective way to form these gaps^3,4. We have investigated the 2 salts most commonly used throughout the literature as aggregating agents. Their absorption spectra were measured over time as the nanoparticles gradually aggregate and fall out of suspension, as well as their effects on SERS spectra. It was found that adding these salts to colloidal silver nanoparticles causes them to form large clusters which provide huge enhancement to the SERS spectra. This is due to the analyte molecules being situated in newly formed “hot spots” between the nanoparticles. This method is shown to be a cheap and simple way to achieve very large SERS enhancement.

A theoretical analysis of nanoscale metallic hole filled with a dielectric material is presented. The dispersion characteristics of the guided modes of a dielectric-filled metallic nanohole show interesting characteristics such as negative dispersion which is not normally observed in air-filled structures. Moreover, the material dispersion, taken fully into consideration, is shown to have a significant effect on the modal dispersion of guided modes, specially, at visible range of frequencies. The analysis is carried out using a full vectorial finite element method which can accurately detect the propagation properties of the structure under investigation.