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International audience; Monolithic silica sol-gel glasses doped with platinum(II) acetylide complexes possessing respectively four or six phenylacetylene units (PE2-CH2OH and PE3-CH2OH) in combination with various concentrations of spherical and bipyramidal gold nanoparticles (AuNPs) known to enhance non-linear optical absorption, were prepared and polished to high optical quality. The non-linear absorption of the glasses was measured and compared to glasses doped solely with AuNPs, a platinum(II) acetylide with shorter delocalized structure, or combinations of both. At 532 nm excitation wavelength the chromophore inhibited the non-linear scattering previously found for glasses only doped with AuNPs. The measured non-linear absorption was attributed to reverse saturable absorption from the chromophore, as previously reported for PE2-CH2OH/AuNP glasses. At 600 nm strong nonlinear absorption was observed for the PE3-CH2OH/AuNPs glasses, also attributed to reverse saturable absorption. But contrary to previous findings for PE2-CH2OH/AuNPs, no distinct enhancement of the non-linear absorption for PE3-CH2OH/AuNPs was observed. A numerical population model for PE3-CH2OH was used to give a qualitative explanation of this difference. A stronger linear absorption in PE3-CH2OH would cause the highly absorbing triplet state to populate quicker during the leading edge of the laser pulse and this would in turn reduce the influence from two-photon absorption enhancement from AuNPs.

Silicon nano-crystals have been studied intensively due to their photoluminescence properties and possible applications in new generation opto-electronic devices. Their importance in lightning and display technologies is increasing due to the abundance and non-toxicity of silicon. Here we report a single batch solution based synthesis route to silicon nano-crystal organic hybrid films exhibiting white light photoluminescence at room temperature upon excitation by ultraviolet light. Films prepared by ethylene glycol terminated Si nano-crystals showed maximum 240 nm red shift in photoluminescence response upon excitation at 350 nm. The shift was found to decrease in order for hybrid films fabricated using acrylic acid, 1-octanol acid and oleic acid terminated Si nano-crystals. The mean size of the Si nano-crystals (~ 2–10 nm) estimated by Raman spectroscopy were smallest for the ethylene glycol capped Si nano-crystal films. The calculated Tauc bandgaps of the hybrid films varied between 1.51 and 2.35 eV.

New light sources such as LED lamps have the potential to reduce the electricity for lighting significantly. However, by reducing the electricity for lighting, the building heating demand is increased. The effects on the building energy balance of changing to more efficient light sources has been investigated by dynamic thermal modelling of typical Swedish single-family and multi-family residential houses. The results show savings on an average of 3.5 kWh/m 2 and 0.62 €/m 2 for single-family houses, and 3.4 kWh/m 2 and 0.61 €/m 2 for apartments in multi-family houses annually when changing from incandescent and halogen lamps to LED lamps.

Advanced Driver Assistance Systems (ADAS) and Automated Driving (AD)vehicles rely on a variety of sensors and among them optical sensors. Extensivetesting of functions using optical sensors is required and typically performedat proving grounds like AstaZero. Soft surrogate targets are used for safetyreasons but the optical and geometrical characteristics of soft car targets maydiffer considerably from that of real vehicles. During tests the quality of thesoft car targets deteriorates due to repeated impacts and reassembly of thetargets, and there is a need of methods for securing the quality of the softcar targets over time. One of the main goals of the HiFi Visual Target project isto develop and validate accurate and repeatable measurement methods of theoptical and geometric characteristics of soft car targets. HiFi Visual Target

International audience; Monolithic sol–gel silica composites incorporating platinum-based chromophores and various types of gold nanoparticles (AuNPs) are prepared and polished to high optical quality. Their photophysical properties are investigated. The glass materials show well-defined localized surface plasmon resonance (SPR) absorbance from the visible to NIR. No redshifts of the AuNP plasmon absorption peaks due to the increase in nanoparticle doping concentration are observed in the glasses, proving that no or very small SPR coupling effects occur between the AuNPs. At 600 nm excitation, but not at 532 nm, the AuNPs improve the nonlinear absorption performance of glasses codoped with 50 × 10−3 m of a Pt-acetylide chromophore. The glasses doped with lower concentrations of AuNPs (2–5 μm average distance) and 50 × 10−3 m in chromophore, show a marked improvement in nonlinear absorption, with no or only small improvement for the more highly AuNP doped glasses. This study shows the importance of excitation wavelength and nanoparticle concentration for composite systems employing AuNPs to improve two-photon absorption of chromophores.

The dynamic response of a near infrared Ferroelectric Liquid Crystal based Mueller matrix ellipsometer (NIR FLC-MME) is presented. A time dependent simulation model, using the measured time response of the individual FLCs, is used to describe the measured temporal response. Furthermore, the impulse response of the detector and the pre-amplifier is characterized and included in the simulation model. The measured time-dependent intensity response of the MME is reproduced in simulations, and it is concluded that the switching time of the FLCs is the limiting factor for the Mueller matrix measurement time of the FLC-based MME. Based on measurements and simulations our FLC based NIR-MME system is estimated to operate at the maximum speed of approximately 16 ms per Mueller matrix measurement. The FLC-MME may be operated several times faster, since the switching time of the crystals depends on the individual crystal being switched, and to what state it is switched. As a demonstration, the measured temporal response of the Mueller matrix and the retardance of a thick liquid crystal variable retarder upon changing state is demonstrated., to be published in Journal of Modern Optics 20 pages, 6 figures

Mueller matrix ellipsometers (MMEs) are known to be less affected by noise if the compensators have a 132° phase shift between the slow and fast axis. This paper reports on the design and characterization of two custom-made achromatic compensators with minimal deviation from 132° retardation as a function of wavelength. The compensators are based on the dual Fresnel rhomb geometry. One pair was made of CaF2 and the other of fused silica. These materials were selected due to their extended transparency range and optical quality. The CaF2 compensators were experimentally characterized in the 450–8000 nm range, whereas the less IR-transparent fused silica prisms were characterized between 450 and 1900 nm. Both kinds of retarders possessed the necessary properties needed for a broad-band achromatic Mueller matrix ellipsometer, since they were both shown to give well-conditioned system matrices within the measured wavelength regions. Specifically, the condition number for the dual prisms used as a Polarization...

Photodynamic therapy (PDT) is a noninvasive treatment for solid malignant and flat tumors. Light activated sensitizers catalyze photochemical reactions that produce reactive oxygen species which can cause cancer cell death. In this work we investigated the photophysical properties of the photosensitizer ruthenium(II) porphyrin (RuP), along with its PDT efficiency onto rat bladder cancer cells (AY27). Optical spectroscopy verified that RuP is capable to activate singlet oxygen via blue and red absorption bands and inter system crossing (ISC) to the triplet state. In vitro experiments on AY27 indicated increased photo-toxicity of RuP (20μM, 18h incubation) after cell illumination (at 435nm), as a function of blue light exposure. Cell survival fraction was significantly reduced to 14% after illumination of 20μM RuP with 15.6J/cm(2), whereas the "dark toxicity" of 20μM RuP was 17%. Structural and morphological changes of cells were observed, due to RuP accumulation, as well as light-dependent cell death was recorded by confocal microscopy. Flow cytometry verified that PDT-RuP (50μM) triggered significant photo-induced cellular destruction with a photoxicity of (93%±0.9%). Interestingly, the present investigation of RuP-PDT showed that the dominating mode of cell death is necrosis. RuP "dark toxicity" compared to the conventional chemotherapeutic drug cisplatin was higher, both evaluated by the MTT assay (24h). In conclusion, the present investigation shows that RuP with or without photoactivation induces cell death of bladder cancer cells.

International audience; Silica-based hybrid materials doped with gold nanoparticles (AuNPs) of different shapes were prepared with an adapted sol–gel technology (using MTEOS) and polished to high optical quality. Both spherical (23 and 45 nm in diameter) and bipyramidal (36, 50 and 78 nm in length) AuNPs were prepared and used as dopants. The AuNPs were functionalized with a novel silicone polymer for compatibilization with the sol–gel medium. The glass materials showed well defined localized surface plasmon resonance (SPR) absorbance from the visible to NIR. No redshifts in the spectra, due to the increase in doping concentration, were observed in the glasses, proving that no or very small SPR coupling effects occur. Spectroscopic Muller Matrix Ellipsometry showed that the shorter bipyramidal AuNPs (36 and 50 nm in length) have a clear preferred orientation in the MTEOS matrix, i.e. a tendency to be oriented with their long axis in the plane parallel to the glass surfaces. Dispersions of AuNPs have proven to be good optical power limiters that depend on particle size and geometry. The solid-state glass materials showed good optical power limiting at 532 nm for nanosecond pulses, which did not depend on the size or geometry of the AuNPs. In contrast to the observation at 532 nm, at 600 nm no optical limiting effect was observed. In these solids, as for dispersions of AuNPs, the optical limiting response is caused by scattering.

Phase modulating spatial light modulators (SLMs) can be used to alter the shape of a laser wavefront to achieve a deflection or change in the shape of a laser beam. This paper reports the results of characterization, simulation and optimization of a one-dimensional liquid crystal (LC) SLM. The device has a large ratio between LC layer thickness and pixel pitch that results in a fringing field between pixels. In effect, the applied phase patterns will be lowpass filtered and the loss of high frequency components limits, for instance, the usable steering range. A method is presented where intensity measurements in the far field are used to determine how the phase modulation at the SLM is distorted. The inhomogeneous optical anisotropy of the device was determined by modelling the liquid crystal director distribution within the electrode-pixel structure. Finite-difference time-domain (FDTD) simulations were used to calculate the light propagation through the LC. The simulated phase distortion was co...

Fluorinated hyperbranched polymers and dendrimers with low optical losses and functionality to modify refractive index and add a cross-linking unit were developed. The results of refractive index measurements indicate a tunability of the refractive index between approximately 1.5 and 1.6, and optical losses below 0.5 dB/cm at 1550 nm. Dendrimers with similar surface group structure and possibility to surface functionalization were prepared using a lanthanide cation as focal point. Results on luminescent properties in the NIR and IR regions were measured for lanthanide ions such as Nd3+ and Er3+, showing characteristic emission bands at 1.06, 1.3 and 1.5 μm. The associated absorption and excitation spectra were found similar to those of the corresponding ions in optical glasses.

A scheme based on the Cranck–Nicholson model has been realized in Matlab code and used to simulate the intensity propagation of various temporal pulse shapes through optically nonlinear materials. The differential equations associated with three- and five-level systems were solved numerically in each point over the active time–space grid. Instantaneous two-photon absorption and dynamic multilevel systems, one at the time, or in combination, can be used to model material responses. A typical Rayleigh length was 0.5 mm and a pulse length up to a few nanometers for sample lengths of typically 2 mm.

We report second harmonic generation in a ferroelectric liquid crystalline trimer and ferroelectric liquid crystalline dendrimers of first, second and third generation. Thin cells were filled with the compounds by capillary forces at elevated temperature, and cooled from the surface stabilized ferroelectric state to below the glass transition temperature, while kept in an electric field. The cone motion viscosity and the threshold electric field for unwinding of the helix axis of the chiral tilted smectic mesophases were studied separately at elevated temperature, and these data were used to optimize the preparation of the films. The measured response time was between 0.3 and 3ms, which corresponds to a cone motion viscosity between 0.5 and 50 Pa s. Second harmonic generation was studied both at elevated temperature with an electric field and at room temperature with and without electric field. The first generation dendrimer exhibited a strong increase in the second order non-linear optical response with time at room temperature. The d 23-coefficient of this dendrimer was approximately four times larger than for the other macromolecules and was 0.045 pm V-1. The relatively large d-coefficient of the first generation dendrimer is ascribed to crystallization, which improved the orientation of the molecular dipoles.

We present electro-optic switching from a planar waveguide with a ferroelectric liquid crystal overlayer and discuss the operating principle and the parameters significant for the operation of the device. We have found electro-optic response times of about 20 μs at best as well as a high (5.7%) transmittance in the ON-state of the device. The contrast ratio was 4:1 ON to OFF state.

A theoretical model describing the fluence-dependent absorption of Gaussian shaped laser beams by optically thick nonlinear media is applied to the interpretation of Z-scan measurements with thick samples of chloro-aluminium-phthalocyanine. The results obtained from the measurements and the modeling have produced an enhanced understanding of the nonlinear processes operating within this type of material, as well as the role of the relaxation mechanisms and saturation effects in shaping the nonlinear absorption, and the optical limiting capability of this type of absorber. An exact first-order analysis of a five-level molecular model has been developed and explored for the case where the incident beam possesses a flat temporal profile. The predictions of the model are in excellent agreement with experimental observations and with results produced from a numerical modeling technique, previously developed, where a simple "relaxation-free" and "population-saturation-free" three-level model is used to predict the transmission properties of a thick five-level system.

A new class of materials, denoted Pyroelectric Liquid Crystal Polymers (PLCP), is described in this work. It is a polymer which is thermodynamically stable, intrinsically polar and suitable for sec...

A numerical approach to analyze the z-scan measurement has been developed for non-Gaussian laser beams. The new approach is based on a mode expansion of the electric field of the laser beam into Gaussian-Laguerre or Gaussian-Hermite modes. The individual modes, appropriate for a laser beam entering the sample, are propagated within the non-linear sample under the influence of the irradiance dependent phase-shifts. The resulting electric field at the exit plane is expanded as a new sum of Gaussian-Laguerre or Gaussian-Hermite modes. The output from one sample can be used as input in a second sample, and hereby the method makes it possible to simulate a variety of complex optical limiting devices. Here we focus the attention to nonlinear optical limiting devices based on two samples, i.e., a tandem limiter. Theoretical simulations are compared with experimental data.

We present the use of correlation analysis on spectral data in order to quantify the amount of a given spectrum present with respect to a reference spectrum. The method is shown to be useful in analyzing hyperspectral fluorescence images. It is unhindered by the linear relationship assumed in linear spectral unmixing, and in addition, it is shown to be robust with respect to noise. Hyperspectral analysis using the correlation between image and reference © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

High quality, j/sub c/ (77 K)>10/sup 6/ A/cm/sup 2/, epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-x/ films of 50 nm thickness were patterned into ten parallel 1 /spl mu/m wide strips. The film structure was coupled to a single-mode fiber. Mixer response was obtained at 0.78 /spl mu/m using laser frequency modulation and an optical delay line. Using two semiconductor lasers at 1.55 /spl mu/m wavelength the beating signal was used to measure the photoresponse up to 18 GHz. Nonequilibrium photoresponse in the resistive state of the superconductor was observed. Bolometric response dominates up to 3 GHz, after which the nonequilibrium response is constant up to the frequency limit of our registration system. Using an electron heating model the influence of different thermal processes on the conversion loss has been analyzed. Ways of increasing the sensitivity are also discussed. >

Picosecond nonequilibrium and slow bolometric responses to infrared radiation from a patterned high-T c superconducting (HTS) film in resistive and normal states deposited onto LaAlO3, NdGaO3, and MgO substrates were investigated using both pulse and modulation techniques. The response time of 35 ps to a laser pulse of 17 ps FWHM has been observed. The intrinsic response time of the fast process is expected to be about a few picoseconds. The modulation technique, being free from the disadvantages of pulse methods (poor sensitivity, limited dynamic range), makes the detailed study of a number of relaxation processes possible. Besides the nonequilibrium response, two kinds of bolometric processes, namely phonon transport through the film-substrate interface and phonon thermal diffusion in a substrate, manifest themselves in certain frequency dependences.

Epitaxial laser deposited YBa2Cu3O7−δ films of ∼50 nm thickness were patterned into detectors consisting of ten parallel 1 μm wide strips in order to study nonequilibrium and bolometric effects. Typically, the patterned samples had critical temperatures around 86 K, transition widths around 2 K and critical current densities above 1×106A/cm2 at 77 K. Pulsed laser measurements at 0.8 μm wavelength (17 ps full width at half maximum) showed a ∼30 ps response, attributed to electron heating, followed by a slower bolometric decay. Amplitude modulation in the band fmod=100 kHz–10 GHz of a laser with wavelength λ=0.8 μm showed two different thermal relaxations in the photoresponse. Phonon escape from the film (∼3 ns) is the limiting process, followed by heat diffusion in the substrate. Similar relaxations were also seen for λ=10.6 μm. The photoresponse measurements were made with the film in the resistive state and extended into the normal state. These states were created by supercritical bias currents. Measurem...

Films (0.5–2 μm thickness) of PMMA doped with (t-Bu)4-Pb-phthalocyanine (Pbpc) in the concentration range 0–100% have been studied as multilayer slab waveguides. Multilayer waveguides were made by spin-coating PMMA/Pbpc solutions onto a polyimide system (PIQ). Using the prism coupling method in an m-line set-up, the guiding TE and TM modes were investigated at two wavelengths, 1064 and 514.5 nm, the latter being in the optical window of Pbpc. The value of the refractive index of PMMA/Pbpc was found to be larger at 1064 nm, and in addition anisotropic, the latter indicating partial ordering. It is suggested that the plane of the Pbpc rings tends to be oriented preferentially parallel to the film plane. The results demonstrate the possibility of using a phthalocyanine/polymer system as an active nonlinear waveguide device operating in the optical window (λ: ∼ 515 nm). Dispersion relations for uniaxial three- and four-layered waveguide geometries, and field distributions of the eigenmodes were derived and used to design (simulate) basic optically-nonlinear waveguide applications in organic multilayer structures. It is shown how the unique properties of Pbpc (an optical window with low value of n) enables phase-matched SHG for TEω → TE2ω for modes of the same order, giving optimal overlap and high conversion.

Fluorescence recovery after photobleaching (FRAP) is a widely used method to measure diffusion. The technique is normally based on one-photon excitation, which limits diffusion to two dimensions due to extended photobleaching in the axial direction. Multiphoton excitation, on the other hand, creates a well-defined focal volume. In the present work, FRAP based on a scanning laser beam and two-photon excitation is used to measure diffusion of macromolecules in solution and gels, as well as in the extracellular matrix in multicellular spheroids and tumor tissue in dorsal chambers. The bleaching profile is determined experimentally in immobilized gels, and for small scanning areas (approximately twice the lateral radius of the laser beam) a Gaussian bleaching distribution is found. In addition, the bleaching profile is determined theoretically based on the convolution of the Gaussian point spread function and a circular scanning area. The diffusion coefficient is determined by fitting a mathematical model based on a Gaussian laser beam profile to the experimental recovery curve. The diffusion coefficient decreases with increasing complexity of the sample matrix and increasing the amount of collagen in the gels. The potential of using two-photon laser scanning microscopes for noninvasive diffusion measurements in tissue is demonstrated.

Results from an experimental polarimetric investigation of 7 different types of land mines and 3 types of plants with the aim to explore the possibility in discriminating surface land mines from natural backgrounds are presented. The reflection Mueller matrices at both specular and non-specular angles at 405 nm and 1570 nm laser illumination were collected. Also included in this study are reflection spectra from the mines taken from 400 to 2500 nm, as well as actual images of surface land mines hidden in a natural environment during different weather conditions. The mines had a reflection coefficient between 5-15 % with peak values around 510 nm due to the embedded green pigment. The mines were found to be less reflective in wet compared to dry conditions. The polarimetric study revealed that the samples had similar retardance and diattenuation values for small incident angles, but that discrimination between the samples could be made by monitoring the depolarization of the incident light for several incident angles, as a function of the angular distribution of scattered light. The land mines generally experience less depolarization than the investigated plants, specifically for specular angles around 1570 nm where the mines act as a non-depolarizing sample with depolarization index close to 1.0. The depolarization index is significantly smaller for specular angles from the plants, becoming 0.4 or below. Both plants and mines experience more depolarization for non-specular angles. A non-specular angular scan with a constant bi-static angle resulted in a Lorentzian shaped depolarization index curve, with characteristic differences in the fitted line-shape parameters. Remote laser based polarimetry might thus be a promising supplementary technique in recognizing surface mines or other related man-made objects from a natural background. Conclusively, the depolarization index as a function of angular distribution of scattered light along with its wavelength dependence is a metric that produce significant differences in the polarimetric signatures.

Characteristic changes in the organization of fibrillar collagen can potentially serve as an early diagnostic marker in various pathological processes. Tissue types containing collagen I can be probed by pulsed high-intensity laser radiation, thereby generating second harmonic light that provides information about the composition and structure at a microscopic level. A technique was developed to determine the essential second harmonic generation (SHG) parameters in a laser scanning microscope setup. A rat-tail tendon frozen section was rotated in the xy-plane with the pulsed laser light propagating along the z-axis. By analyzing the generated second harmonic light in the forward direction with parallel and crossed polarizer relative to the polarization of the excitation laser beam, the second-order nonlinear optical susceptibilities of the collagen fiber were determined. Systematic variations in SHG response between ordered and less ordered structures were recorded and evaluated. A 500 microm-thick z-cut lithiumniobate (LiNbO(3)) was used as reference. The method was applied on frozen sections of malignant melanoma and normal skin tissue. Significant differences were found in the values of d(22), indicating that this parameter has a potential role in differentiating between normal and pathological processes.

We present results of a measurement system designed for detecting the fluorescence spectrum of individual aerosol particles of biological warfare agents excited with laser pulses at wavelengths around 290 or 340 nm. The biological aerosol is prepared and directed into a narrow air beam. A red laser is focused on the aerosol beam and a trigger photomultiplier tube monitor the presence of individual particles by measuring the scattered light. When a particle is present in the detection volume, a laser pulse is triggered from an ultraviolet laser and the fluorescence spectrum is acquired with a spectrometer based on a diffraction grating and a 32 channels photomultiplier tube array with single-photon sensitivity. The spectrometer measures the fluorescence spectra in the wavelength region from 300 to 800 nm. In the experiment we used different simulants of biological warfare agents. These bioaerosol particles were excited by a commercial available gas laser (337 nm), or a laser (290 nm) that we have developed based on an optical parametric oscillator with intracavity sum-frequency mixing. In the analysis of the experiments we compare the measured signals (fluorescence spectra, total fluorescence energy and the scattered energy) from the individual bioaerosol particles excited with the two different ultraviolet wavelengths.

Highly ordered hexagonal arrays of isoporous films prepared from poly(9,9'-dihexylfluorene) and polystyrene-grafted silica nanoparticles (Si-graft-PS) are presented. These close-packed arrays were formed in areas of many square millimeters. The pore size varied from 3.6 to 8.5 microm, depending on the concentration of Si-graft-PS and the processing conditions. Solid-state photoluminescence resulted in a significant red shift of up to 30 nm in these films compared to that in conventional processing techniques. These differences are attributed to enhanced aggregation of the polymers caused by polymer-solvent interactions. These highly ordered polymer films may find use in microelectronic and biological and/or chemical sensor applications.

We present initial results of a measurement system designed for detecting the fluorescence spectrum of individual particles of biological warfare agent (BWA). A compact optical parametric oscillator with intracavity sum-frequency mixing and a commercial Nitrogen gas laser was used as excitation sources to generate 293 nm or 337 nm UV laser irradiation. The pulsed lasers and a photomultiplier tube (PMT) array based spectrometer were triggered by a red laser-diode and a PMT detector that sensed the presence of a particle typical of size 5-20 μm in diameter. The spectral detection part of the system consisted of a grating and a PMT array with 32 channels, which measured fluorescence in the wavelength from 280 nm to 800 nm. The detector system was used to demonstrate the measurement of laser induced fluorescence spectra of individual BWA simulant particles by excitation of single UV laser pulses. The spectrum obtained by averaging spectra from several BWA aerosol simulant particles were found generally similar, but not identical, to the fluorescence spectrum obtained from water solutions containing the same particles dissolved.

We report on the initial time-resolved luminescense and nonlinear absorption properties of two polythiophenes 3-substituted with chiral charged amino acid-derivatized substituents, POWT and POMT. The photo-physical characterization yielded quantum efficiency typically in the range 0.01 - 0.1, however, with two-photon absorption cross-section better than or similar to a typical two-photon reference chromophore, such as fluorescein. They were tested as conformational sensitive optical probes for the recording of pH-induced conformational changes of synthetic peptides, proteins and samples of protein amyloid fibrils characteristic of amyloid related diseases. Particularly, the POMT polyelectrolyte with the L-enantiomeric side chains is shown to favor this induction of well defined structure as judged by the circular dichroic signal as well as a stronger enhancement of luminescense for the L-form over the D-form complex. Furthermore, time-resolved fluorescense and two-photon induced fluorescence both also showed a difference in the complexation with the D and L form. This shows that the multi-photon excitation path can be an efficient means for chiral recognition of biomolecular complexes. It is demonstrated how the conjugated polyelectrolyte L-POMT can be used to spectrally image the formation of amyloid fibrils of insulin using both one- and two-photon absorption based fluorescence imaging.

The polarization properties of a nematic zero-twist liquid-crystal (NLC) spatial light modulator (SLM) were studied. A large ratio between the liquid-crystal (LC) layer thickness and the pixel pitch combined with spatial variations in the applied electric field causes fringing fields between pixels. Depending on the LC alignment, the electric field components within the LC layer can result in a twist deformation. The produced inhomogeneous optical anisotropy affects the polarization of light propagating through the device. We experimentally examined polarization effects in different diffraction orders for both binary and blazed phase gratings. Simulations of the LC deformation together with finite-difference time-domain simulations for the optical propagation were used to calculate the corresponding far-field intensities. It was demonstrated how rigorous simulations of the NLC SLM properties can be used to understand the polarization features of different diffraction orders.

Results of our on-going development of biological warfare agents (BWA) detection systems based on spectral detection of ultraviolet (UV) laser induced fluorescence (LIF) are presented. A compact optical parametric oscillator (OPO) with intracavity sum-frequency mixing (SFM) to generate 293 nm UV laser irradiation was developed. The OPO/SFM device was pumped by a diode-pumped Nd:YAG laser (1064 nm), including subsequent second-harmonic generation (SHG) in an external periodically poled KTiOPO4 (PPKTP) crystal. The laser generated 1.8 ns pulses at 100 Hz with an average power of 44 mW at 532 nm. The whole system could be used to deliver approximately 30 μJ laser irradiation per pulse (100 Hz) at 293 nm. The spectral detection part of the system consists of a grating and a photomultiplier tube (PMT) array with 32 channels, which can measure fluorescence spectra in the wavelength band from 250 nm to 800 nm. The detector system was designed along with a trigger laser to enable measurement of fluorescence spectra from an individual aerosol particle of simulants for BWA upon excitation with a single nanosecond laser pulse. We demonstrate the successful detection and spectral characterization of simulants for BWA, i.e., Bacillus atrophaeus (BG), Bacillus thuringiensis (BT), and Ovalbumin (OA).

Hot‐electron bolometric (HEB) mixing of 9.6 μm infrared radiation from two lasers in high‐quality YBa2Cu3O7−δ (YBCO) patterned thin film has been demonstrated. A heterodyne measurement showed an intermediate frequency (IF) bandwidth of 18 GHz, limited by our measurement system. An intrinsic limit of 100 GHz is predicted. Between 0.1 and 1 GHz intermediate frequency, temperature fluctuations with an equivalent output noise temperature Tfl up to ∼150 K, contributed to the mixer noise while Johnson noise dominated above 1 GHz. The overall conversion loss at 77 K at low intermediate frequencies was measured to be ∼25 dB, of which 13 dB was due to the coupling loss. The HEB mixer is very promising for use in heterodyne receivers within the whole infrared range.

This paper presents the status of an ongoing development of a point detector for biological warfare agent sensing based on ultraviolet laser-induced fluorescence from single particles in air. The detector will measure the fluorescence spectra of single particles in a sheath flow air beam. The spectral detection part of the system consists of a grating and a photomultiplier tube array with 32 channels, which measure fluorescence spectra in the wavelength band from 300 nm to 650 nm. The detector is designed to measure laser induced fluorescence from single laser pulses and has been tested by measuring fluorescence from simulants of biological warfare agents in aqueous solution. The solutions were excited with laser pulses at the wavelengths of 293 nm and 337 nm. The paper also presents preliminary results on the sheath flow particle injector and time-resolved measurements of fluorescence from biological warfare agent simulants in solution.

A novel, compact and robust UV laser has been developed for laser induced fluorescence spectroscopy of biomolecules in the spectral region from 290 nm to 345 nm. It was based on a frequency-doubled passively Q-switched Nd:YAG laser, emitting at 532 nm, which was pumping a periodically poled KTiOPO 4 optical parametric oscillator with intra-cavity sum-frequency mixing in a BBO crystal. The output was generated in two branches in the UV, 293 nm and 343 nm, with pulse widths of 1.8 ns and pulse repetition rate of 100 Hz. These wavelengths were then used for fluorescence experiments of bioagents. Keyword list : diode pump solid-state laser, optical parametric oscillator, parametric devices, ultra violet generation. 1. INTRODUCTION Laser technology is widely used in the field of biochemi stry and biotechnology for det ection and characterization of biomolecules. Fluorescence based techniques are applied in studies of everything from protein folding to DNA sequencing. The spectral response from these biomolecules have specific signatures that can be used for identification. Usually, protein molecules and nucleotides fluoresce following UV excitation in the approximate range 280 - 340 nm.

A simulator (GSIM) for missile seekers that can be used as a general tool in missile seeker performance analysis has been developed. The simulator contains all the subsystems of a typical missile system and can simulate a missile flight scenario from launch, via target acquisition and tracking, to arrival at the target. GSIM has a fully graphical user interface and runs under Matlab on a regular modern PC. Due to a modular approach, the simulator can easily be upgraded and adapted to different prerequisites. It contains a choice of targets against sky, sea or ground backgrounds. Weather conditions, visibility, and time-of-day are taken into account when seeker images are generated. The effects of detector noise and dome heating are also modeled. The results can be presented as movies from the flight, showing both the seeker image as well as trajectories for the missile and target.

The use of liquid crystal spatial light modulators in applications, require good characterization of phase, polarization and amplitude shifting properties. This report presents a new approach for simultaneously characterizing the depolarization and controlling the polarization properties of a reflective twisted nematic liquid crystal spatial light modulator (LC SLM). The SLM was set up as a part of a Michelson interferometer. The phase response was determined by using a piezo-electric actuator for phase stepping in the reference arm. During the polarization measurement the reference beam was removed and the polarization state of the input and output was determined by a polarization state generator (PSG) and a polarization state analyzer (PSA), each consisting of a polarizer and a quarter-wave plate. Hereby, both phase response and polarization control properties could be determined independently in the same measurement configuration simply by changing static polarization components. The systematic rotation of the quarter wave plates of the PSG and the PSA using stepper motors gives out-put data whose Fourier transform in terms of angular frequency components can be used to determine all the elements of the Mueller matrix. The Mueller matrix of a commercial SLM (Holoeye LC-2500) was determined for 17 evenly spaced voltage levels addressed to the SLM.

A compact parametric oscillator (OPO) with intracavity sum-frequency generation (SFG) to generate 293 nm UV laser irradiation, was developed. The OPO/SFG device was pumped by a 100 Hz Nd:YAG laser (1064 nm) of own design, including subsequent second harmonic generation (SHG) in an external periodically poled KTiOPO 4 (KTP) crystal. The whole system could be used to deliver more than 30 μJ laser irradiation per pulse (100 Hz) at 293 nm. The UV laser light was introduced in an optical fiber attached to a sample compartment allowing detection of fluorescence emission using a commercial spectrometer. Aqueous samples containing biomolecules (ovalbumin) or bacteria spores ( Bacillus subtilis ) were excited by the UV-light at 293 nm resulting in strong fluorescence emission in the range 325 - 600 nm.

A commercial linear one-dimensional, 1x4096 pixels, zero-twist nematic liquid crystal spatial light modulator (SLM), giving more than 2π phase modulation at λ = 850 nm, was evaluated for beam steering applications. The large ratio (7:1) between the liquid crystal layer thickness and pixel width gives rise to voltage leakage and fringing fields between pixels. Due to the fringing fields the ideal calculated phase patterns cannot be perfectly realized by the device. Losses in high frequency components in the phase patterns were found to limit the maximum deflection angle. The inhomogeneous optical anisotropy of the SLM was determined by modelling of the liquid crystal director distribution within the electrode-pixel structure. The effects of the fringing fields on the amplitude and phase modulation were studied by full vector finite-difference time-domain simulations. It was found that the fringing fields also resulted in coupling into an unwanted polarization mode. Measurements of how this mode coupling affects the beam steering quality were carried out and the results compared with calculated results. A method to compensate for the fringing field effects is discussed and it is shown how the usable steering range of the SLM can be extended to ± 2 degrees.

Optical parametric oscillator (OPO) and sum-frequency mixing (SFM) devices are useful tools for constructing ultraviolet (UV) laser sources for fluorescence spectroscopy. Here, a compact UV-laser sources based on frequency conversion of an actively Q-switched Nd:YAG laser is presented. The second harmonic generation from a Nd:YAG laser was utilized as pump radiation for a periodically poled KTiOPO 4 nanosecond optical parametric oscillator 1 . The OPO-signal and the remaining pump were spatially mode-matched for Type I SFM in a β-barium borate (BBO) crystal and UV radiation at 293 nm could be generated. This corresponds to a conversion efficiency of 2 % with respect to the 532 nm harmonic radiation. The wavelength region accessible with this UV source is useful for chemical and biological sensing. Excitation of tryptophan at 293 nm for detection of fluorescence emission in ovalbumin and transthyretin was demonstrated.

A linear one-dimensional, 1x4096 pixel, zero-twist nematic liquid crystal spatial light modulator (SLM) was evaluated for laser beam steering and tracking applications. The commercially obtained SLM is designed to operate at, λ = 850 nm, allowing more than 2 π phase modulation. Due to voltage leakage the phase modulation experienced by the wave front differed from the ideal calculated phase patterns. This cross talk between pixels reduces the diffraction efficiency. Different methods developed to compensate for this effect are presented. The usable steering range of the SLM was extended to ± 2 degrees using improved phase patterns. A simple model was developed to simulate the optical effects of the voltage leakage. Preliminary tracking experiments were carried out in a laboratory set-up using a moving corner cube retro reflector. The beam steering SLM was implemented in a transceiver for free-space optical communication. Initial results using the transceiver up to 180 m range are presented.

We report on the development of methods and equipment which facilitates the measurement of the Modulation Transfer Function (MTF) of IR optics exposed to both high and low temperatures. The MTF is a very powerful measure of the quality of any optical system, and is a common way to test the performance. However, because of the large apparatus needed to perform the testing it is generally not possible to measure the MTF at temperatures other than room temperature. A thermally insulating enclosure was designed in which the optics under test is placed on a temperature-controlled fixture. The enclosure permits the radiation to reach the optics under test and allows the MTF measurement probe to reach the image plane. Meanwhile the MTF measurement bench is kept at room temperature. In this way it is possible to vary the temperature of the optics under test between -30 °C and +85 °C and simultaneously measure the MTF. Using the same equipment it is also possible to measure bore sight error, ensquared energy, and focus position as a function of temperature. A commercially available MTF measurement bench was specially adapted for this purpose. Measurements can be made both on- and off axis and both MWIR and LWIR measurements are possible.

Mixing of 1.56 μm infrared radiation from two lasers in a high quality YBa2Cu3O7−δ thin film, patterned to parallel strips, was demonstrated. A mixer bandwidth of 18 GHz, limited by the measurement system, was obtained. A model based on nonequilibrium electron heating gives a good fit to the data and predicts an intrinsic mixer bandwidth in excess of 100 GHz, operating in the whole infrared spectrum. Reduction of bolometric effects and ways to decrease the conversion loss of the mixer is discussed. The minimum conversion loss is expected to be ∼10 dB.

Thin YBa2Cu3O7−δ laser deposited films were patterned into devices consisting of ten parallel 1 μm wide strips. Nonequilibrium picosecond and bolometric photoresponses were studied by the use of 17 ps full width at half‐maximum laser pulses and amplitude modulated radiation from an AlGaAs laser up to 10 GHz and from a CO2 laser up to 1 GHz. The time and frequency domain measurements were in agreement. The fast response can be explained by electron heating. The use of low optical power and a sensitive measurement system excluded any nonlinear transient processes and kinetic inductance changes in the superconducting state. At 1 GHz modulation frequency, the responsivity was ∼1.2 V/W both for 0.8 and 10.6 μm wavelengths. The sensitivity of a fast and spectrally broadband infrared detector is discussed.

Detectors for infrared radiation ( lambda =0.85 mu m) were made of 50 nm thick YBa2Cu3O7- delta films on LaAlO3 and MgO or 60 nm thick films on NdGaO3. Parallel strips (1 mu m wide by 20 mu m long) were patterned in the films and formed the active device. These devices were designed to detect short infrared laser pulses by electron heating. The detectors were current biased into the resistive and the normal states. The response was studied in direct pulse measurements as well as by amplitude modulation of a laser. The pulse measurements showed a fast picosecond response followed by a slower decay related to phonon escape through the film-substrate interface and heat diffusion in the substrate. The frequency spectra up to 10 GHz showed two slopes with a knee corresponding to the phonon escape time.

We report on optical transmission properties and results of optical waveguide characterization of flourinated hyperbranched polymers and dendrimers (details on chemical synthesis were reported recently [1]). The polymers and dendrimers allow the introduction of additional functionality, such as cross-linking and refractive index tuneability. The dendrimers having a similar bulk structure as the hyperbranched polymer were also shown to house lanthanide cations for optical amplifying application. The fluorinated bulk structure results in a low contribution from vibration overtones in the absorption spectra in the NIR/IR region (800 - 2200 nm). The refractive index of the fundamental fluorinated hyperbranched polymer was found to be tuneable between ca 1.45 and 1.65 by incorporating various substituents. Optical losses were measured to be below ca 0.5 dB/cm at 1550 nm.

The spatial light modulator (SLM) can be used to alter the phase of the wave front to achieve a deflection or a change in the shape of a laser beam. In this study a commercial nematic zero-twist liquid crystal SLM was evaluated. SLMs can be operated to produce pure phase modulation necessary for beam steering. For liquid crystals the relation between applied voltage and phase modulation is highly non-linear due to the relation between the voltage driven molecular tilt angle and extraordinary refractive index. To compensate for this effect we optimized and examined look-up tables (LUT) that realize the inverse of the phase response. It was found that the factory LUT improved the power ratio between the zero order and the first order peaks five times compared to the case without using an LUT, however, further improvement of this ratio of two was reached using an LUT optimized from the measured phase response of the SLM. The discrete phase modulation results in a stepped, non-ideal blazed grating that alters the relative power of the available steering angles. To obtain optimal performance these effects must be analyzed for different bit depths and preliminary results of such quantization effects are discussed.

We report the preparation and characterization of novel isotropic polymer slab waveguides made by photochemical crosslinking, and their integration with a ferroelectric liquid crystal in an integra ...

The response from a high Tc superconducting multielement optical detector made of a laser deposited Y-Ba-Cu-O thin film has been evaluated. Several microscopic and spectroscopic techniques were used to establish the presence of the correct phase of the thin film. Optical pulses from a laser diode at 830 nm and from a Q-switched CO2-laser at 10.6 microns were used. The detector responded to 50 ps (FWHM) pulses. A comparison between dR/dT of the film and the response amplitude as a function of temperature indicated a bolometric response.

M-line measurements have been performed on thin films of pyroelectric liquid crystalline polymers (PLCP), in order to determine the magnitude and anisotropy of the refractive index. The films, polymerized under various conditions, are based on materials exhibiting a chiral smectic C phase. The results of the measurements were analyzed and compared with a new numerical method to model the optical properties of anisotropic multilayered thin films. In the model, which is an extension of the analytical approach of Berreman, the eigenmodes and boundary conditions of refracted light waves are handled and solved by numerical matrix manipulations. Model calculations of total reflection measurements for various multi-layered systems were used to investigate the effect of ITO and polyimide aligning layers to the apparent effective index of m-lines.

A numerical scheme for modeling of z-scans with samples ranging from thin samples to beyond the thick sample limit was introduced in our previous work (A. Eriksson et al., J. Opt. Soc. Am. B15, pp. 810-816, 1998). The method relies on a multilayer approach, where all layers are treated as independent, and may have different linear and nonlinear optical properties. The theoretical scheme can be used for irradiance as well as fluence, dependent absorbers. It allows for an arbitrarily shaped aperture in front of the detector. Here the method is tested and compared with the results of analytical thick sample theory and previously published numerical simulations. Ways of optimizing the performance of an optical limiting device are modeled and discussed. Preliminary experimental z-scan results of both thin and thick sample chloro-aluminum phthalocyanine were analyzed.