An analysis of ray-tracing schemes in the mid-IR range through the main model forms of rough and polished diamonds used for determining content of basic defects based on optical absorption measurements has been carried out. It is shown that in the traditional transmission measurement scheme only a small fraction of the radiation incident on the crystal is detected due to refraction and scattering in many crystals, leading to decreasing of the signal-to-noise ratio and to narrowing of the signal levels dynamic range. Practical recommendations are given and optimal variants of ray-tracing schemes through the most characteristic crystal shapes are proposed. This makes it possible to detect the maximum fraction of the radiation transmitted through the crystal, and to implement effective measurements of optical absorption in a wide dynamic range to determine the concentrations of basic defects with a high signal-to-noise ratio.

An experimental study of nonlinear absorption process of ultrashort laser pulses in bulk of natural diamond has been carried out. The results of experimental studies on measuring nonlinear transmission of 1 mm thick plane-parallel plate made of diamond irradiated with focused by micro lens (NA=0.55 with focal length f'=5 mm) 0.3 and 10 ps laser pulses with 1030 nm wavelength are presented. It is shown that in this sample the main attenuation mechanism of ultrashort laser pulses with 1030 nm wavelength at intensities not exceeding 10 TW/cm2 is two-photon absorption at color centers, the absorption coefficient β2 =4.1 ± 0.3 cm/TW is determined.

A study of high-NA focusing process of ultrashort laser pulses in bulk of ZnSe has been carried out. It is shown that when focusing laser Gaussian beam with high-aperture lenses into a transparent medium aberration distortions occur leading to an increase in focal spot size. The results of experimental studies on ablation of front and back surfaces of a plane-parallel plate with 4 mm thickness made of ZnSe by laser pulses with a duration of 0.3ps, 1ps, 10ps and a wavelength of 1030nm focused by a micro lens (NA=0.55) are presented. It is shown that at low pulse energies focusing can be considered in a linear mode in which focal spot size is due to aberration distortions.

AbstractThe basic principles of a multichannel model of the visual system of a human that functions as an operator performing surveillance on images formed by optoelectronic devices are described. A technique for experimental studying the model of the human visual system is proposed. The results of experimental studies aimed refining the parameters of the model of the visual system are presented. A satisfactory agreement between the calculated and experimental results indicates that the refined model of the human visual system is adequate.