The presence of characteristic peaks in the terahertz (THz) absorption spectra of many organic substances and the active development of the technology for manufacturing video cameras based on microbolometric matrices create an increased interest in methods for identifying explosive compounds using THz imaging with simultaneous recording of spectral information. The results of relevant studies can be used in the development of security systems. THz images (taking into account the spectral information in each pixel) were obtained in this work by passing radiation through a sample based on hexogen (RDX) microcrystals deposited on a polyethylene (PE) film. A photoconductive antenna was used as a source of broadband radiation in the range from 0.5 THz to 2.5 THz. Spectral resolution was provided using a Fourier spectrometer based on a Michelson interferometer. The images were recorded using a THz video camera based on a microbolometric matrix. The possibility of identifying RDX microcrystals using color visualization of spectral information in the frequency range of one of the characteristic RDX peaks (~0.8 THz) has been demonstrated.
The work is devoted to the influence of scattering of terahertz (THz) radiation by hexogen particles (RDX) in powdery samples on their transmission and reflection spectra. A terahertz radio-vision installation with spectral resolution was used to determine experimentally THz spectra of RDX. For samples with small RDX particles (the typical particle size is 100 μm), characteristic peaks at 0.8 THz and 1.06 THz are observed in absorption spectra despite scattering, that can be used to identify this substance. For large hexogen particles (a typical particle size is 450 μm), experiments and numerical simulation showed that even the most intense peak at 0.8 THz is not observed in absorption spectra, and the spectra are mainly due to the scattering effect and its depending on the wavelength of radiation. The reflection spectra of RDX layers (particle size is about 100 μm) qualitatively differ from the reflection spectra of RDX crystals and are formed as a result of absorption during propagation of THz radiation in the particle layer. Thus, the substance can be identified by absorption spectra in a reflection scheme.
The paper presents the results of application of terahertz radiation for detection of traces of explosives on surfaces of objects in reflected light. The process of detection and identification of explosives is based on a recording of interferograms of reflected radiation in spectral range of 0.5 -2.5 THz with help of a Michelson interferometer. The reverse Fourier processing lets to obtain reflection or transmittance spectra and images of objects. Spectral ranges for imaging are chosen by an operator. An installation elaborated for this purpose is described. Specific features of reflection spectra of some organic substances are determined.