The paper presents analyses of current research projects connected with explosive material sensors. Sensors are described assigned to X and γ radiation, optical radiation sensors, as well as detectors applied in gas chromatography, electrochemical and chemical sensors. Furthermore, neutron techniques and magnetic resonance devices were analyzed. Special attention was drawn to optoelectronic sensors of explosive devices.

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The polymorphism of resorcinol has been complementary studied by combining Raman, time-domain terahertz, and inelastic neutron scattering spectroscopy with modern solid-state density functional theory (DFT) calculations. The spectral differences, emerging from the temperature-induced structural phase transition, have been successfully interpreted with an emphasis on the low-wavenumber range. The given interpretation is based on the plane-wave DFT computations, providing an excellent overall reproduction of both wavenumbers and intensities and revealing the source of the observed spectral differences. The performance of the generalized gradient approximation (GGA) functionals in prediction of the structural parameters and the vibrational spectra of the normal-pressure polymorphs of resorcinol has been extensively examined. The results show that the standard Perdew, Burke, and Ernzerhof (PBE) approach along with its "hard" revised form tends to be superior if compared to the "soft" GGA approximation.

Abstract. We report on a method for extracting the characteristic features of covered materials, including hexogen, in the range from 0.5 to 1.8 THz. This time-domain spectroscopy-based technique takes into account only part of the signal reflected from a covered sample and analyzes it by using the Fourier transform. The obtained power spectrum has distinctive peaks that correspond to peaks measured in the transmission configuration and can be used for further identification of the materials. © IntroductionTerahertz (THz) radiation in the range of 0.3 to 3.0 THz has a strong potential for use in identification of covered explosive materials because of two key factors. Some commonly used explosive materials, such as hexogen (RDX), octogen (HMX), and penthryte (PETN) possess distinctive transmission 1,2 and reflection 3,4 spectral features (called "fingerprints") in the THz regime. Also, most commonly used nonpolar dielectric covering materials, such as cotton, polyester, paper, and plastic materials, show low absorption of THz waves. Since the attenuation properties of most explosive materials are relatively high, 2 the transmission configuration seems to be more applicable to samples that are a few millimeters thick, e.g., for use in mail scanners. In contrast, the reflection configuration is safer for inspection applications and is more suitable for performing detection on people and inside envelopes or bags. However, the reflection configuration is more complicated owing to the small reflectance from pure explosive materials, 4 the strong attenuation properties of water vapor, the scattering effects related to the morphology of the sample 5,6 as well as to the attenuation properties of the covering layers.

In this paper we present an extensive theoretical and numerical analysis of monolithic high-index contrast grating, facilitating simple manufacture of compact mirrors for very broad spectrum of vertical-cavity surface-emitting lasers (VCSELs) emitting from ultraviolet to mid-infrared. We provide the theoretical background explaining the phenomenon of high reflectance in monolithic subwavelength gratings. In addition, by using a three-dimensional, fully vectorial optical model, verified by comparison with the experiment, we investigate the optimal parameters of high-index contrast grating enabling more than 99.99% reflectance in the diversity of photonic materials and in the broad range of wavelengths.

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Terahertz and infrared radiation have unique properties applicable to the field of surveillance and security systems. We investigated the possibility of detecting potentially dangerous objects covered by various types of clothing using passive imagers operating at 1.2 mm (250 GHz) and long-wavelength infrared at 6-15 μm (20-50 THz). We developed a measurement methodology that assumes to investigate theoretical limitations, performance of imagers, and physical properties of fabrics. To evaluate stability of the detection capabilities of imagers, we performed measurement sessions each lasting 30 min. We present a theoretical comparison of the two spectra and results of experiments using state-of-the-art equipment.

We report on the terahertz analysis of an internal structure of an ultra-high molecular weight polyethylene (UHMWPE) composite material, which is based on the HB10-tape from Dyneema . This type of composite is very hard and resistant and therefore it is often used to manufacture personal armors such as bulletproof vests and helmets. The multilayer structure of the UHMWPE composite was investigated by means of a raster scanning time domain spectroscopy technique in a reflection configuration. The mechanism of the formation of many shifted in time THz pulses (reflected from the internal layers of the sample) originates from the periodic modulation of the refractive index along the propagation of the radiation. This modulation is connected with alternate layers of fibers, each having different direction (perpendicular to each other). As a result we obtained the detailed three dimensional profile of the 3.3-mm thick sample with all 74 layers clearly visible. Thicknesses of all layers, having around 45 µm each, were determined. Moreover, it is also possible to identify internal defects i.e. delaminations in the internal structure of this composite material.