Volume 127, Nº 4 (2019)

Overtone bands in the spectral range of 1300−1920 cm^–1 have been found in Raman scattering spectrum of lithium tantalate single crystals. The Raman spectra were recorded in the 180° scattering geometry. The intensity of overtone transitions differs for different samples and, in some cases, is comparable with the Raman scattering intensity at the fundamental modes of a lithium tantalate single crystal.

Raman spectra of tryptophan and tyrosine polycrystals have been analyzed in a wide spectral range by fiber-optic spectroscopy. The Raman spectra have been recorded with a BWS465-785H spectrometer in the spectral range of 0–2700 cm^–1 using a 785-nm cw laser as an excitation source. Parameters of the Raman spectra are compared for three crystalline phase modifications of aromatic amino acids: left-handed, right-handed, and racemic phase. The presence of strong Raman satellites, the characteristics of which change depending on the type of the chiral phase state of amino acid, is found in the low-frequency Raman spectra of tryptophan and tyrosine amino acid lattices. The results obtained can be used for monitoring the chiral purity of bioactive preparations containing amino acids.

The ratio between energies of Vavilov–Cherenkov radiation and cathodoluminescence excited by an electron beam in diamond samples is determined taking into account electron scattering in these samples, energy distribution of beam electrons, ionization losses of the electron energy, and dispersion of the diamond refractive index. Experimental results on measuring spectral characteristics of the glow of natural and synthetic diamond samples under the action of a subnanosecond electron beam with electron energy of up to 200 keV are presented. It is shown that most of the radiation of the diamond samples in the region of 240–750 nm under the action of an electron beam with electron energy of up to 200 keV belongs to cathodoluminescence.

A comparative analysis of various implementations of multichannel recording using optical filters is performed to improve the spectral resolution of multichannel hyperspectrometers at maintaining the high spatial resolution. The computing power of different means of multichannel data processing is considered as well. The recovery of spectral brightness density using multichannel recording data is shown to be an incorrect task. The methods proposed to solve it are wavelet transformation, Tikhonov’s regularization approach, and Godunov method. The spectral brightness density is simulated using the multichannel recording results taking into account the measurement error. The applicability limits are established for each method. It is supposed that the Tikhonov method is more resistant to measurement errors. Various approaches for selecting optical filters that participate in the multichannel recording are compared with respect to the final accuracy of spectral brightness density reconstruction using the recording data, which evidences the benefits of the classical method. The optimal combination of the amount of optical filters and the number of recording channels is found as well. The wide application necessitates three channels with four optical filters and eight channels with two optical filters.

A rational method for calculating the transmission of light by a thin metal screen with an infinite periodic array of subwavelength slits is proposed. The calculation results agree well with available experimental and theoretical data.

Characteristic features of anisotropic light diffraction in a spatially periodic acoustic field created by a sectioned piezoelectric transducer with antiphase excitation of adjacent sections are studied theoretically. The numerical calculation is carried out for a cell of a paratellurite crystal with a shear acoustic mode propagating at an angle of 3° to the (001) plane of the crystal. It is shown that this type of acoustooptic interaction has some interesting features that can be used when developing acoustooptic devices, in particular, modulators of nonpolarized light.

An algorithm that automatically calculates aberrations in the holographic wavefront sensor scheme previously proposed by the authors is described, which enables measuring aberrations by means of iterative generation of holograms on a phase spatial light modulator (SLM). The practical implementation of this algorithm on the basis of the feedback of the camera and SLM is given. Using the proposed algorithm, defocusing was measured with an accuracy of λ/160.

Nonlinear refraction in a number of crystals (KGW, KGW:Eu³⁺, Ba(NO₃)₂, BaWO₄, PbMoO₄, and CdWO₄) that are promising for excitation of multifrequency stimulated Raman scattering is investigated by a single-beam Z-scan method. Picosecond laser pulses with a wavelength of 1064 nm generated by a YAG:Nd³⁺ laser were used for excitation of nonlinear optical processes. The values of n₂ are compared depending on the type of the crystal, optical-axis orientation, and impurity concentration.

Nonlinear absorption of a probe field in a system of degenerate levels of an atom characterized by a total moment of J = 1 in unidirectional waves is studied analytically and numerically taking into account saturation by its own spontaneous emission (OSE). The trends in changes of the amplitude and frequency characteristics of the nonlinear resonance associated with open and closed types of transitions for different polarizations of the waves that are introduced by self-saturation are established. Specific manifestations of the effect, including those related to magnetic coherence of levels, are revealed.

The problem of reinforcing the mirror surfaces of space-based astronomical optics and their protection against external factors is discussed. To solve this problem, the possibility of the deposition of diamond-like coatings onto them is considered. Using mirrors with Al and Cu coatings as an example, it has been experimentally demonstrated that the pulsed laser deposition of a carbon layer with a thickness of 30 nm onto them leads to an increase in the surface hardness by 25 and 100%, respectively. It has been established that the reinforcing coating has no effect on the shape deviations of mirrors and decrease their surface roughness. In this case, the reflection factor appreciably decreases in the visible region (400–780 nm), whereas its decrease in the infrared region (above 780 nm) is no more than 5%.

A methodology has been developed for measuring radius R_v and eccentricity (conic parameter k) of large concave aspherical mirrors using a wavefront sensor. Analytical expressions that directly relate Zernike coefficients a₄ and a₉ to parameters R_v and k of the mirror are obtained. It is shown that the technique does not require accurate mirror alignment before measurements. A computer analysis showed that the developed scheme enables measurements with errors of δR_v < 0.1% and δk < 0.01 for mirrors with radii from 100 to 2000 mm and with errors of δR_v < 0.01% and δk < 0.001 for mirrors with radii of more than 5000 mm.

The influence of the laser frequency drift on the operation of phase-sensitive optical time domain reflectometry (φ-OTDR) systems is considered. Theoretical results based on a new numerical φ-OTDR model demonstrating the influence of the laser frequency instability on a signal are reported. This model is verified based on experimental data. It has been used to calculate the signal-to-noise ratio (SNR) of the system for different parameters of the laser source stability. As a result, quantitative requirements for lasers used in φ-OTDR systems are formulated.

The testing of an all-fiber erbium ultrashort pulsed laser in a distributed fiber temperature sensor as a source of probing pulses has been performed. Among the prospects of such an approach are an improved signal–noise ratio in the receiving system and a better spatial resolution of the temperature sensor. The experiments have revealed the factors that limit the effective length of the fiber temperature sensor, such as a high pulse repetition frequency and intrinsic laser noises. As a result of the performed work, the distributed fiber optical temperature sensor with a near-room-temperature resolution of ~1.5 K, an effective length of ~3 m, and a spatial resolution of ~10 cm has been developed.

The tracking of hydrodynamic disturbances within the sea surface and near-surface layer and surface layer aerosol is performed using three different installations, a laser locator, photometer of sea brightness, and elastic aerosol lidar. The experiments are carried out under the natural conditions of the Black Sea polygon. A surface vessel was a source of hydrodynamic perturbations in the form of a lagging track. The results reveal the efficiency of the methods used to record ship tracks in three media.

The 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.

Pinhole model measurement errors in 3D triangulation based scanners is studied in the present work. Pupil aberrations of the scanner lenses are shown to cause noticeable errors in determining the coordinates of surface points. The requirements for aberration characteristics are formulated to minimize the error of 3D scanners. A modification of the pinhole model allowing a decrease in the error induced by pupil aberration of lenses of triangulation-based scanners is proposed as well.

Spin-exchange cross sections and the magnetic-resonance frequency shift in collision of lithium and potassium atoms in the ground state have been calculated for the first time. The cross sections are calculated based on the data on the singlet (\(X{}^{1}{{\Sigma }^{ + }}\)) and triplet (\(a{}^{3}{{\Sigma }^{ + }}\)) interaction potentials of ³⁹K⁷Li dimer. A passage from the energy dependences to the temperature ones of the real and imaginary parts of the complex spin-exchange cross section yields information about both the broadening of the magnetic resonance line of the atoms under study and the magnetic-resonance frequency shift in their collision.

A method is proposed for precise measurement of the deflection of the magnetic field vector. This method does not require the use of artificially created magnetic fields; a scheme of an all-optical quantum sensor based on this method has been experimentally tested. The proposed method does not involve the use of radiofrequency field, since it is based on measuring the polarization properties of an oriented paramagnetic medium and does not use the phenomenon of magnetic resonance. However, the inclusion of a resonant radiofrequency field into the proposed scheme allows the information about the angle of the magnetic field vector to be supplemented with information about its module. The proposed method maintains operability and provides the same angular sensitivity of the order of tens of angular milliseconds in a wide range of magnetic fields, from hundreds of nT to hundreds of µT and above.