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The possibility of using the lenses with an aspherical surface for terahertz/ sub-terahertz (THz/sub-THz) imaging systems has been considered. Diffraction-limited optical system of four identical plano-convex aspheric lenses has been obtained. Tests of the lenses have been performed on the specially made stand. These calculated and experimental data have similar values, which confirms the use of such lenses in the THz/ sub-THz imaging systems. [ABSTRACT FROM AUTHOR]

Room temperature linear arrays (up to 160 detectors in array) from silicon metaloxide-semiconductor field-effect transistors (Si-MOSFETs) have been designed for sub-THz (radiation frequency 140 GHz) close to real-time direct detection operation scanner to be used for detection and recognition of hidden objects. For this scanner, the optical system with aspherical lenses has been designed and manufactured. To estimate the quality of optical system and its resolution, the system modulation transfer function was applied. The scanner can perform real-time imaging with the spatial resolution better than 5 mm at the radiation frequency 140 GHz and contrast 0.5 for the moving object speed up to 200 mm/s and the depth of field 20 mm. The average dynamic range of real time imaging system with 160-detector linear array is close to 35 dB, when the sources with the output radiation power of 23 mW (IMPATT diodes) are used (scan speed 200 mm/s). For the system with 32-detector array, the dynamic range was about 48 dB and for the single-detector system with raster scanning 80 dB with lock-in amplifier. However, in the latter case for obtaining the image with the sizes 20×40 mm and step of 1 mm, the average scanning time close to 15 min is needed. Convolutional neural network was exploited for automatic detection and recognition of hidden items. [ABSTRACT FROM AUTHOR]

Two-color un-cooled narrow-gap MCT (mercury-cadmium-telluride) semiconductor thin layers, grown by liquid phase epitaxy or molecular beam epitaxy methods on high resistivity CdZnTe or GaAs substrates, with bow-type antennas were considered both as sub-terahertz direct detection bolometers and 3 . . . 10-micrometer infrared photoconductors. Optical system with aspheric THz lenses were designed and manufactured. An antenna pattern of structures on the thick substrate was discussed, and sensitivity of detector in both IR and sub-THz regions was measured. [ABSTRACT FROM AUTHOR]