This PDF file contains the front matter associated with SPIE Proceedings Volume 9253, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

A method for detecting ultralow quantities of explosives in air and explosive traces using a state-of-the-art picosecond chip Nd³⁺:YAG laser has been elaborated. The method combines field asymmetric ion mobility spectrometry (FAIMS) with laser ionization of air samples and laser desorption of analyzed molecules from examined surfaces. Radiation of the fourth harmonic (λ = 266 nm, τ_pulse = 300 ps, E_pulse = 20-150 μJ, ν = 20-300 Hz) was used. The ionization efficiencies for trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), and glyceryl trinitrate (NG) were investigated. The dependences on frequency, pulse energy, peak intensity, and average power for TNT and RDX were determined. It was shown that the optimal peak intensity should be no less than 2∙106 W/cm²; at lower peak intensities, the increase of the average laser power in the interval 5–15 mW enhanced the ion signal. The results of detection of TNT, RDX, and NG vapors under these conditions were compared with the results obtained using nanosecond laser excitation. The detected ion signals for all explosives were shown to be two- to threefold higher in the case of picosecond excitation. The FAIMS laser desorption regime was developed where a laser beam exiting the detector after removal of a special plug was used. The results of TNT and RDX detection are presented. The chip Nd³⁺:YAG laser has a small emitter and a consumed electric power of 25 W. The estimated detection threshold of the prototype picosecond laser FAIMS analyzer of explosives is (1-3)∙10^-15g/cm³ for TNT vapors.

We report the results of Raman investigation performed at stand-off distance between 6-10 m with a new apparatus, capable to detect traces of explosives with surface concentrations similar to those of a single fingerprint. The device was developed as part of the RADEX prototype (RAman Detection of EXplosives) and is capable of detecting the Raman signal with a single laser shot of few ns (10^-9 s) in the UV range (wavelength 266 nm), in conditions of safety for the human eye. This is because the maximum permissible exposure (MPE) for the human eye is established to be 3 mJ/cm² in this wavelength region and pulse duration. Samples of explosives (PETN, TNT, Urea Nitrate, Ammonium Nitrate) were prepared starting from solutions deposited on samples of common fabrics or clothing materials such as blue jeans, leather, polyester or polyamide. The deposition process takes place via a piezoelectric-controlled plotter device, capable of producing drops of welldefined volume, down to nanoliters, on a surface of several cm², in order to carefully control the amount of explosive released to the tissue and thus simulate a slight stain on a garment of a potential terrorist. Depending on the type of explosive sampled, the detected density ranges from 0.1 to 1 mg/cm² and is comparable to the density measured in a spot on a dress or a bag due to the contact with hands contaminated with explosives, as it could happen in the preparation of an improvised explosive device (IED) by a terrorist. To our knowledge the developed device is at the highest detection limits nowadays achievable in the field of eyesafe, stand-off Raman instruments. The signals obtained show some vibrational bands of the Raman spectra of our samples with high signal-to-noise ratio (SNR), allowing us to identify with high sensitivity (high number of True Positives) and selectivity (low number of False Positives) the explosives, so that the instrument could represent the basis for an automated and remote monitoring device.

We have recently developed methods for making more accurate infrared total and diffuse directional - hemispherical reflectance measurements using an integrating sphere. We have found that reflectance spectra of solids, especially powders, are influenced by a number of factors including the sample preparation method, the particle size and morphology, as well as the sample origin. On a quantitative basis we have investigated some of these parameters and the effects they have on reflectance spectra, particularly in the longwave infrared. In the IR the spectral features may be observed as either maxima or minima: In general, upward-going peaks in the reflectance spectrum result from strong surface scattering, i.e. rays that are reflected from the surface without bulk penetration, whereas downward-going peaks are due to either absorption or volume scattering, i.e. rays that have penetrated or refracted into the sample interior and are not reflected. The light signals reflected from solids usually encompass all such effects, but with strong dependencies on particle size and preparation. This paper measures the reflectance spectra in the 1.3 – 16 micron range for various bulk materials that have a combination of strong and weak absorption bands in order to observe the effects on the spectral features: Bulk materials were ground with a mortar and pestle and sieved to separate the samples into various size fractions between 5 and 500 microns. The median particle size is demonstrated to have large effects on the reflectance spectra. For certain minerals we also observe significant spectral change depending on the geologic origin of the sample. All three such effects (particle size, preparation and provenance) result in substantial change in the reflectance spectra for solid materials; successful identification algorithms will require sufficient flexibility to account for these parameters.

We propose effective criteria based on the analysis of spectral dynamics of medium response for the detection and identification of dangerous substances at using pulsed THz signal containing a few cycles and fixed absolute phase. These criteria are integral criteria in time. We show the applicability of these criteria for distinguishing the drugs and for drugs detection in the mixture with neutral substances and explosives in transmission mode. We also apply these criteria for the detection of PWM C4 explosive with complicated shape of the surface in reflection mode.

A handheld bottle checker for detection of liquid explosives is developed using near infrared technology. In order to make it compact, a LED light was used as a light source and a novel circuit board was developed for the device control instead of using a PC. This enables low power consumption and this handheld detector can be powered by a Li-ion battery without an AC power supply. This checker works well to analyze liquids, even using limited bandwidth of NIR by the LED. It is expected that it can be applied not only to airport security but also to wider applications because of its compactness and portability.

Millimeter (mm)and sub-mm wavelengths or terahertz (THz) band have several properties that motivate their use in imaging for security applications such as recognition of hidden objects, dangerous materials, aerosols, imaging through walls as in hostage situations, and also in bad weather conditions. There is no known ionization hazard for biological tissue, and atmospheric degradation of THz radiation is relatively low for practical imaging distances. We recently developed a new technology for the detection of THz radiation. This technology is based on very inexpensive plasma neon indicator lamps, also known as Glow Discharge Detector (GDD), that can be used as very sensitive THz radiation detectors. Using them, we designed and constructed a Focal Plane Array (FPA) and obtained recognizable2-dimensional THz images of both dielectric and metallic objects. Using THz wave it is shown here that even concealed weapons made of dielectric material can be detected. An example is an image of a knife concealed inside a leather bag and also under heavy clothing. Three-dimensional imaging using radar methods can enhance those images since it can allow the isolation of the concealed objects from the body and environmental clutter such as nearby furniture or other people. The GDDs enable direct heterodyning between the electric field of the target signal and the reference signal eliminating the requirement for expensive mixers, sources, and Low Noise Amplifiers (LNAs).We expanded the ability of the FPA so that we are able to obtain recognizable 2-dimensional THz images in real time. We show here that the THz detection of objects in three dimensions, using FMCW principles is also applicable in real time. This imaging system is also shown here to be capable of imaging objects from distances allowing standoff detection of suspicious objects and humans from large distances.

The spectral properties of THz pulses containing a few cycles reflected from a flat metallic mirror placed at long distance about 3.5 meters from the parabolic mirror are investigated. The samples for analysis were placed before this mirror. Measurements were provided at room temperature of about 18-20° C and humidity of about 70%. The aim of investigation was the detection of a substance under real conditions. At the present time our measurements contain features of both transmission and reflection modes. This leads to a strong modulation of the spectrum and makes difficulties for identification. As samples for our current research we used several neutral substances: paper layers, a thick paper bag, chocolate and cookies. The first problem deals with the detection of common and mismatched spectral properties of samples with paper layers, a thick paper bag and explosives. HMX, PETN and RDX were used as explosive samples. The dependence of the accuracy of identification of samples with paper layers and a thick bag is studied when using short transmitted THz signals with opposite absolute phases as calibration signals. Common and mismatched spectral features of neutral substances: chocolate, cookies and drugs MA, MDMA were investigated by modified integral criteria as well.

A novel method is introduced for distinguishing counterfeit banknotes from genuine samples. The method is based on analyzing differences in the networks of paper fibers. The main tool is a curvelet-based algorithm for measuring the distribution of overall fiber orientation and quantifying its anisotropy. The use of a couple or more appropriate parameters makes it possible to distinguish forgeries from genuine samples as concentrated point clouds in a two- or three-dimensional parameter space. Furthermore, the techniques of making watermarks is investigated by comparing genuine and counterfeit €50 banknotes. In addition, the so-called wire markings are shown to differ significantly from each other in all of investigated banknotes.

The real manifestations of biowarfare were only during local military conflicts. In previous times the danger with this factor forms through activation of terrorist organizations. To prevent non-desirable consequences and to preserve the lives and health of people it is necessary to provide constant control by the application of complex of the new generation of the instrumental devices based on the principles of biosensorics which allow rapid revealing step by step: total toxicity of environmental objects, presence of appropriate groups and specific chemical substances among them. It is demonstrated simple and rapid estimation of the total toxicity through the control of the intensity of chlorophyll fluorescence (IChF) by the direct or remote ways by the device “Floratest” (Ukraine). There is possible on the basis of IChF curve of growing plants from some territory during appropriate period to reveal appearance of toxic substances in this area. Their presence in more local cases may be done by using bioluminescent bacteria (pure Ukrainian strains) or/and controlling short term Daphnia living medium by developed portable chemiluminometer. For the revealing of some groups of toxic elements it is recommended the cerium oxide ISFETs based enzymatic biosensors. The last and devices based on SPR (“Plasmotest”, Ukraine), porous silicon (with the registration of biospecific interaction macromolecules by luminescence or electro conductivity) and some nano-metal oxides were realized in immune biosensors at the determination of content of number of mycotoxins, some microorganisms (Salmonella spp.) and diagnostics of viral disease (retroviral leucosis). We present the main characteristics of the above mentioned devices and give confirmation that all the analysis meets practice demands. Overall time of analysis is in range 10 min and it is very simple and may be realized in field conditions.

We propose a stand-off system that enables detection and classification of CBRNe (Chemical, Biological, Radioactive, Nuclear aerosol and explosive solids). The system is an integrated lidar using a high-power (terawatt) femtosecond laser. The detection and classification of various hazardous targets with stand-off distances from several hundred meters to a few kilometers are achieved by means of laser-induced breakdown spectroscopy (LIBS) and two-photon fluorescence (TPF) techniques. In this work, we report on the technical considerations on the system design of the present hybrid lidar system consisting of a nanosecond laser and a femtosecond laser. Also, we describe the current progress in our laboratory experiments that have demonstrated the stand-off detection and classification of various simulants. For the R and N detection scheme, cesium chloride aerosols have successfully been detected by LIBS using a high-power femtosecond laser. For the B detection scheme, TPF signals of organic aerosols such as riboflavin have clearly been recorded. In addition, a compact femtosecond laser has been employed for the LIBS classification of organic plastics employed as e-simulants.

The thermal (emitted) infrared frequency bands, typically from 20-40 THz and 60-100 THz, are best known for applications in thermography, such as target acquisition, surveillance, night vision, and remote sensing. This unregulated part of the spectral range offers opportunities for the development of short-range secure communications. The ‘THz Torch’ concept was recently demonstrated by the authors. This technology fundamentally exploits engineered blackbody radiation, by partitioning thermally-generated spectral noise power into pre-defined frequency channels. The energy in each channel is then independently pulse-modulated, transmitted and detected, creating a robust form of short-range secure communications in the far/mid infrared. In this paper, recent progress for the ‘THz Torch’ technology will be presented; the physical level integrity for multichannel proof-of-concept working demonstrators will be evaluated. By exploring a diverse range of methods, significant enhancements to both data rate and distance can be expected. Our thermodynamics-based approach represents a new paradigm in the sense that 19th century physics can be exploited with 20th century multiplexing concepts for low-cost 21st century ubiquitous security and defence applications in the thermal infrared range.

Automatic detection of abnormal behavior in CCTV cameras is important to improve the security in crowded environments, such as shopping malls, airports and railway stations. This behavior can be characterized at different time scales, e.g., by small-scale subtle and obvious actions or by large-scale walking patterns and interactions between people. For example, pickpocketing can be recognized by the actual snatch (small scale), when he follows the victim, or when he interacts with an accomplice before and after the incident (longer time scale). This paper focusses on event recognition by detecting large-scale track-based patterns. Our event recognition method consists of several steps: pedestrian detection, object tracking, track-based feature computation and rule-based event classification. In the experiment, we focused on single track actions (walk, run, loiter, stop, turn) and track interactions (pass, meet, merge, split). The experiment includes a controlled setup, where 10 actors perform these actions. The method is also applied to all tracks that are generated in a crowded shopping mall in a selected time frame. The results show that most of the actions can be detected reliably (on average 90%) at a low false positive rate (1.1%), and that the interactions obtain lower detection rates (70% at 0.3% FP). This method may become one of the components that assists operators to find threatening behavior and enrich the selection of videos that are to be observed.

Proactive detection of incidents is required to decrease the cost of security incidents. This paper focusses on the automatic early detection of suspicious behavior of pickpockets with track-based features in a crowded shopping mall. Our method consists of several steps: pedestrian tracking, feature computation and pickpocket recognition. This is challenging because the environment is crowded, people move freely through areas which cannot be covered by a single camera, because the actual snatch is a subtle action, and because collaboration is complex social behavior. We carried out an experiment with more than 20 validated pickpocket incidents. We used a top-down approach to translate expert knowledge in features and rules, and a bottom-up approach to learn discriminating patterns with a classifier. The classifier was used to separate the pickpockets from normal passers-by who are shopping in the mall. We performed a cross validation to train and evaluate our system. In this paper, we describe our method, identify the most valuable features, and analyze the results that were obtained in the experiment. We estimate the quality of these features and the performance of automatic detection of (collaborating) pickpockets. The results show that many of the pickpockets can be detected at a low false alarm rate.

In the quest for greater computer lip-reading performance there are a number of tacit assumptions which are either present in the datasets (high resolution for example) or in the methods (recognition of spoken visual units called "visemes" for example). Here we review these and other assumptions and show the surprising result that computer lip-reading is not heavily constrained by video resolution, pose, lighting and other practical factors. However, the working assumption that visemes, which are the visual equivalent of phonemes, are the best unit for recognition does need further examination. We conclude that visemes, which were defined over a century ago, are unlikely to be optimal for a modern computer lip-reading system.

The capability to find individuals using CCTV cameras is important for surveillance applications at large areas such as railway stations, airports and shopping centers. However, it is laborious to track and trace people over multiple cameras post incident. In this paper, we describe the live demonstration of our interactive re-identification system in a railway station. The system performs real-time track generation in multiple cameras and live re-identification and refinding of suspects which was live demonstrated in Poland. The system allows fast interactive retrieval of an individual by showing only similar candidates. An operator can find the origin or destination of a person more efficiently, especially over large time and space intervals.

Target tracking within conventional video imagery poses a significant challenge that is increasingly being addressed via complex algorithmic solutions. The complexity of this problem can be fundamentally attributed to the ambiguity associated with actual 3D scene position of a given tracked object in relation to its observed position in 2D image space. We propose an approach that challenges the current trend in complex tracking solutions by addressing this fundamental ambiguity head-on. In contrast to prior work in the field, we leverage the key advantages of thermal-band infrared (IR) imagery for the pedestrian localization to show that robust localization and foreground target separation, afforded via such imagery, facilities accurate 3D position estimation to within the error bounds of conventional Global Position System (GPS) positioning. This work investigates the accuracy of classical photogrammetry, within the context of current target detection and classification techniques, as a means of recovering the true 3D position of pedestrian targets within the scene. Based on photogrammetric estimation of target position, we then illustrate the efficiency of regular Kalman filter based tracking operating on actual 3D pedestrian scene trajectories. We present both a statistical and experimental analysis of the associated errors of this approach in addition to real-time 3D pedestrian tracking using monocular infrared (IR) imagery from a thermal-band camera.

Fused night vision systems have been available for a number of years and have matured into practical devices for use by dismounted soldiers. This paper looks at the approaches taken to achieve fused systems and looks at the real world advantages of such systems in complex urban environments with multiple light sources.

Human action recognition has emerged as an important field in the computer vision community due to its large number of applications such as automatic video surveillance, content based video-search and human robot interaction. In order to cope with the challenges that this large variety of applications present, recent research has focused more on developing classifiers able to detect several actions in more natural and unconstrained video sequences. The invariance discrimination tradeoff in action recognition has been addressed by utilizing a Generalized Hough Transform. As a basis for action representation we transform 3D poses into a robust feature space, referred to as pose descriptors. For each action class a one-dimensional temporal voting space is constructed. Votes are generated from associating pose descriptors with their position in time relative to the end of an action sequence. Training data consists of manually segmented action sequences. In the detection phase valid human 3D poses are assumed as input, e.g. originating from 3D sensors or monocular pose reconstruction methods. The human 3D poses are normalized to gain view-independence and transformed into (i) relative limb-angle space to ensure independence of non-adjacent joints or (ii) geometric features. In (i) an action descriptor consists of the relative angles between limbs and their temporal derivatives. In (ii) the action descriptor consists of different geometric features. In order to circumvent the problem of time-warping we propose to use a codebook of prototypical 3D poses which is generated from sample sequences of 3D motion capture data. This idea is in accordance with the concept of equivalence classes in action space. Results of the codebook method are presented using the Kinect sensor and the CMU Motion Capture Database.

This paper presents a novel approach to detect persons in video by combining optical flow based motion analysis and silhouette based recognition. A new fast optical flow computation method is described, and its application in a motion based analysis framework unifying human tracking and detection is outlined. Our optical flow algorithm represents optical flow by grid based motion vectors, which are computed very efficiently and robustly applying template matching. We model the motion patterns of the tracked human and non-human objects by the positions, velocities, motion magnitudes, and motion directions of their optical flow vectors, and build a random forest on these features. For recognition, the random forest computes a normalized score measuring the similarity of a track to a human track. Using edge detection on a motion image for each motion blob its silhouette is computed. Recognition scores are computed, which measure the similarity of the silhouettes with human silhouettes. The optical flow classifier and the silhouette classifier are used as a combined classifier. We analyze the ROC curve to set different decision thresholds on the recognition score for different scenarios. The experiments on the VIRAT test set demonstrate that for human detection the combination of the optical flow based motion method with one based on human silhouette analysis, obtains superior results, compared to the constituent methods.

Human action classification distinguishes different human behaviors at a video signal. Suspicious behavior can be defined by the user, and in long distance imaging it may include bending the body during walking or crawling, in contrast to regular walking for instance. When imaging is performed through relatively long distance, some difficulties occur which affect the performances regular action recognition tasks. The degradation sources that include turbulence and aerosols in the atmosphere cause blur and spatiotemporal-varying distortions (image dancing). These effects become more significant as the imaging distance increases and as the sizes of the objects of interest in the image are smaller. The process of action recognition is usually a part of surveillance system that naturally includes a detection of the moving objects as a first step, followed by tracking them in the video sequence. In this study, we first detect and track moving objects in long-distance horizontal imaging, and then we examine dynamic spatio-temporal (motion and shape) characteristics of correctly detected moving objects. According to such characteristics. We construct features that characterize different actions for such imaging conditions, and distinguish suspicious from non-suspicious actions, based on these characteristics.

Viral infections are of special threat because they can induce severe courses of disease but only few medical treatments are available. Because of socio-economic and climate changes, increased worldwide mobility and population growth, the risk of newly occurring and quickly spreading viral pathogens has increased. A diagnosis of these diseases at an early stage is essential for a quick risk assessment and a proper health management as well as patient’s treatment in an optimal way. Currently, the diagnosis of such diseases is based on time consuming and costly detection methods that can only be performed by specially trained personnel in laboratories at specific security levels. Aim of the project VIROSENS is the development of a biosensor platform that can specifically detect virus particles as well as virus-specific antibodies out of biological matrices like blood, serum, plasma and other body fluids. For this purpose, a disposable cartridge for such antibody- and virus-arrays is designed and developed within the project. The optical detection of viruses is performed with a portable device that will be benchmarked and evaluated concerning currently used standard detection methods in terms of its analytical performance. Within this project, a novel combination of serological tests and direct detection of virus particles will be developed, which will provide faster and more reliable results than presently available and used test systems.

The interplay between photosensitivity and chemical sensitivity can give rise to a number of properties that can extend the sensitivity in each separate context. Here we illustrate how the sensitivity to visble light of porphyrins coated ZnO nanorods can modify the gas detection enhancing the sensitivity in particular towards electron donor species.

In the framework of RAMBO (Rapid-Air Monitoring particle against biological threats) project of the European Defense Agency (EDA), the feasibility of an unattended Surface Enhanced Raman Spectroscopy (SERS) sensor for biological threats detection was investigated. Its main goal concern Bacillus anthrax detection, both as vegetative cells and endospores. However since such bacteria are classified in Risk Group 3 (very dangerous microorganism), Bacillus thuringiensis and Bacillus atrophaeus were used as simulants. In order to bind selectively the target bacilli, Phages properly selected were immobilized on an active commercially available SERS substrate (functionalization). The Phages are a type of virus that infect selectively, by means of receptors, specific bacteria. Moreover they can resist on water or air environments without losing their binding capabilities. The sensing surface was characterized by standard micro-Raman equipments to assess the background Raman features. The Raman measurements have been carried out from 10X to 100X of magnification to differentiate between average and local features. Moreover the fast response was acquired by limiting the measure time at less than 1 minute. Samples of vegetative cells and endospores of Bacilli were randomly dispersed on the functionalized SERS substrates. The results obtained are promising: samples with and without bacilli could be distinguished one from the other. This is a step toward the use of SERS as an effective and fast technique for early warning of biological threats.

Formyl-methoxy derivatives of [2.2]paracyclophane (pCp) have been synthesized and studied by optical spectroscopy as well as the X-ray diffraction method. These molecules crystallize in acentric space groups. The efficiency of SHG ability of these compounds was measured by the powder technique at 1064 nm fundamental wavelength and average NLO susceptibility for some of them was found comparable with such well-known NLO crystal as NPP. The calculations of molecular and crystalline nonlinearities within density functional theory using M052X/6-31+G* level of approximation were also conducted for the considered series of compounds.

The current focus in Swedish policy towards national security and high-end technical systems, together with a rapid development in multispectral sensor technology, adds to the utility of developing advanced materials for spectral design in signature management applications. A literature study was performed probing research databases for advancements. Qualitative text analysis was performed using a six-indicator instrument: spectrally selective reflectance; low gloss; low degree of polarization; low infrared emissivity; non-destructive properties in radar and in general controllability of optical properties. Trends are identified and the most interesting materials and coating designs are presented with relevant performance metrics. They are sorted into categories in the order of increasing complexity: pigments and paints, one-dimensional structures, multidimensional structures (including photonic crystals), and lastly biomimic and metamaterials. The military utility of the coatings is assessed qualitatively. The need for developing a framework for assessing the military utility of incrementally increasing the performance of spectrally selective coatings is identified.

In this paper, we propose ways to study the optical limiting behavior of dissolved nanoparticles. We want to present two different approaches. First, we identify the key properties responsible for the critical fluence threshold using a principal component analysis. For metallic nanoparticles, we found that the real part of the complex dielectric function must have a negative value as low as possible, while the imaginary part must be close to zero. Additionally, the solvent should have a low refractive index as well as a low absorption. Furthermore, nonlinear scattering seems to be an important limiting mechanism for nanoparticle limiters. Here, we present a thermal finite element model to predict the temporal evolution of the temperature profile in the nanoparticles and their vicinity. The temperature profile leads to vapor bubbles around the nanoparticles and Mie theory is used to calculate the induced scattering. We demonstrate the functionality of the model by simulating an Au-nanoparticle in an ethanol solution.

An interest of chalcogenide glass has been increased because of their use in preparing optical lenses in range of 3-12 μm. With recent advance in less costly uncooled detector technology, moldable lens using chalcogenide glass has drawn a great deal of attention. In this study, amorphous Ge-Sb-Se chalcogenide was prepared by a standard melt-quenching technique. Melted chalcogenide glass for moldable lens should have unique thermal and mechanic properties in order to be applied to molding process. Specifically, the Ge:Sb ratio were controlled in order to find out the most stable glass forming area. Thus, the optical, thermal and thermomechanical properties to find out the specific composition were characterized by FT-IR spectroscopy, Differential Scanning Calorimeter and Thermo Mechanical Analysis, respectively. The moldability of chalcogenide glass was characterized through the surface condition of glass samples. Finally, the preferential Ge:Sb ratio in Ge-Sb-Se based chalcogenide glass system was selected to fabricate moldable lenses.

The selectivity of an optical sensor can be improved by combining optical detection with electrochemical oxidation or reduction of the target analyte to change its spectral properties. The changing signal can distinguish the analyte from interferences with similar spectral properties that would otherwise interfere. The analyte is detected by measuring the intensity of the electrochemically modulated signal. In one form this spectroelectrochemical sensor consists of an optically transparent electrode (OTE) coated with a film that preconcentrates the target analyte. The OTE functions as an optical waveguide for attenuated total reflectance (ATR) spectroscopy, which detects the analyte by absorption. Sensitivity relies in part on a large change in molar absorptivity between the two oxidation states used for electrochemical modulation of the optical signal. A critical part of the sensor is the ion selective film. It should preconcentrate the analyte and exclude some interferences. At the same time the film must not interfere with the electrochemistry or the optical detection. Therefore, since the debut of the sensor’s concept one major focus of our group has been developing appropriate films for different analytes. Here we report the development of a series of quaternized poly(vinylpyridine)-co-styrene (QPVP-co-S) anion exchange films for use in spectroelectrochemical sensors to enable sensitive detection of target anionic analytes in complex samples. The films were either 10% or 20% styrene and were prepared with varying degrees of quaternized pyridine groups, up to 70%. Films were characterized with respect to thickness with spectroscopic ellipsometry, degree of quaternization with FTIR, and electrochemically and spectroelectrochemically using the anions ferrocyanide and pertechnetate.

After working for years on organic materials, e.g., polythiophenes and relevant composites with metal nanoparticles, we shifted our attention to unusual metals, chosen as candidates to effective amperometric sensing on the basis of the atomic structure and crystalline properties. The present contribution aims at proposing an electrode material rarely employed in electroanalysis, namely Ti. We have experimented that the peculiar nature of Ti leads to electrochemical behavior quite different with respect to the conventional electrode materials, including those based on TiO₂ (nano)particles. Our work focuses on the determination of strong oxidizing species, namely H₂O₂ and HClO, and noble metal ions, namely Au(III). Strong oxidizing species are commodity chemicals employed in a number of different industrial processes, in which usually high concentration levels should be monitored. The procedures proposed have been successfully applied also in complex matrices, such as detergent samples. As to Au(III) determination, it also constitutes a crucial tool in order to increase the efficiency of hydrometallurgic processes and of the recovery of precious materials from electronic waste. Ti electrodes allow the determination of dissolved Au species in the presence of other metal ions. In any cases the electrodes exhibit reproducible and repeatable electrochemical responses, even in the presence of high concentration of organic fouling species typical of bio-sorption processes.

Triacetone triperoxide (TATP) explosive is one of the most common components of improvised explosive devices which can be prepared from commercially readily available reagents with easier synthetic procedure that is available over the internet. Molecularly imprinted polymer electrochemical sensors can offer highly selective determination of several classes of compounds from wide range of sample matrices in parts per billion levels. Highly sensitive and selective molecularly imprinted polymer electrochemical sensor has been developed for determination of TATP in acetonitrile. Molecular imprinting has been performed via electro-polymerization on to glassy carbon, gold, silver and platinum electrode surface by cyclic voltammetry from a solution of pyrrole functional monomer, TATP template, and LiClO₄ supporting electrolyte. Quantitative differential pulse voltammetric measurements of TATP, with LiClO₄ supporting electrolyte, were performed using the molecularly imprinted polymer modified and bare glassy carbon electrodes in a potential range of -2.0V to +1.0 V (vs. Ag/AgCl). Three-factor two-level factorial design has been used to optimize the monomer concentration at 0.1 mol L^-1, template concentration at 100 mmol L^-1, and the number of cyclic voltammetry scan cycles to 10 cycles, using differential pulse voltammetric current intensity as response variable. The molecularly imprinted polymer modified glassy carbon electrode demonstrated superior selectivity for TATP in the presence of PETN, RDX, HMX, and TNT.

We evaluate multi walled carbon nanotubes decorated with gold or silver nanoparticles suspended in water regarding their nonlinear attenuation characteristics for nanosecond laser pulses. The results are compared to pure multi walled carbon nanotubes. A Q-switched Nd:YAG laser working at a wavelength of 1064 or 532 nm, with a pulse width of 3 ns is used to characterize their optical limiting behaviour by fluence dependent transmittance measurements. Our experiments show that the properties of the hybrid materials, measured at both wavelengths, could be improved compared to plain multi walled carbon nanotubes.

A series of nonlinear materials including GaAs, GaP, and ZnSe have been examined to determine their suitability for non-linear frequency conversion devices (FCD) and more specifically their use as high power, compact and broadly tunable IR and THz sources for defense and security applications. The more mature GaAs was investigated to reveal the causes for the optical losses that restrict achievement of higher conversion efficiency in quasi-phasematched FCD, while the efforts with GaP were oriented in developing simple, cost effective techniques for fabrication of orientation patterned (OP) templates and optimizing the subsequent thick HVPE growth on these templates. Thus, average growth rates of 50- 70 μm/h were achieved in up to 8-hour long experiments. High optical layer quality was achieved by suitable control of the process parameters. The optimal orientation of the pattern was determined and used as essential feedback aiming to improve the template preparation. This led to the production of the first 300-400 μm thick device quality OPGaP. Efforts to suppress the parasitic nucleation during growths with longer duration or to achieve thicker layers by a 2 step growth process were also made. The main challenge with the newer candidate, OPZnSe, was to establish suitable regimes for hydrothermal growth on plain (001) ZnSe seeds grown by chemical vapor deposition. Two different temperature ranges, 330-350 °C and 290-330 °C, were investigated. The mineralized concentration was also manipulated to accelerate the growth in (111) direction and, thus, to improve the growth in (001) direction. The next material in the line is GaN. The traditional HVPE approach will be combined with a growth at low reactor pressure. Growths will be performed in the next sequence: growth on thin GaN layers grown by MOCVD on sapphire wafers, growth on half-patterned GaN templates with different orientations and, finally, growth on OPGaN templates.

This article provides an overview of the photophysical behavior diversity of polymethine chromophores which are ubiquitous in biological imaging and material sciences. One major challenge in this class of chromophore is to correlate the chemical structure to the observed optical properties, especially when symmetry-breaking phenomena occur. With the constant concern for rationalization of their spectroscopy, we propose an extended classification of polymethine dyes based on their ground state electronic configuration using three limit forms namely: cyanine, dipole and bis-dipole. The chemical modifications of the dye and the influence of exogenous parameters can promote dramatic spectroscopic changes that can be correlated to significant electronic reorganization between the three-abovementioned forms. The deep understanding of such phenomena should allow to identify, predict and take advantage of the versatile electronic structure of polymethines.