Vol 27, No 1 (2019)

The aim of this work is to analyze the high-precision measurements of the profile of spectral lines using near-IR diode lasers (DLs). To this end, a multichannel DL spectrometer of high spectral resolution has been developed, calibrated, and put into operation. Special attention is paid to the deviation of the gases studied from ideal behavior. Real CO₂ gas and a mixture of real CO₂:SF₆ gases are used as models.

The four-photon low-frequency light scattering by acoustic vibrations of elastic inclusions in a liquid heterogeneous medium has been investigated. General expressions are obtained for the amplitude of electromagnetic wave generated in the field of specified two-frequency (Raman) optical pumping under conditions of induced longitudinal acoustic vibrations of cylindrical inclusions. The total field radiated by the suspension at a frequency shifted with respect to the pump frequency has been analytically calculated.

It is shown that Fourier transform infrared emission spectroscopy can be used to analyze carotenoids and chlorophyll in whole leaves of cultivated tobacco Nicotiana tabacum L and its two modifications L₁ and L₂. The results show that information on the structure and component composition of plant tissue pigments can be obtained in vivo without the negative effect of water and autofluorescence.

Acousto-optic Q-switched lasing in the crystal Tm:Yb₃Al₅O₁₂ (Tm:YbAG) pumped at the wavelength of 1.678 µm into the ³F₄−³H₆ thulium transition is investigated. The highest differential laser efficiency was 13%. The laser pulse energy was as high as 100 µJ at the optimum pulse repetition rate of 6.7 kHz and monopulse duration of 45 ns. The lifetime of the excited Tm³⁺ ion under intense lasing is experimentally estimated. The effect of upconversion processes on lasing is analyzed.

The correlation function of output laser radiation has been investigated as a function of the spontaneous emission passes number of an active medium in an unstable resonator. The initial incoherent spontaneous emission is represented as a sum of spatially δ-correlated fields formed by point sources. The characteristics of focused output laser beam have been investigated within the Fresnel approximation. The beam width and Strehl ratio have been analyzed as a function of the number of spontaneous-emission passes and resonator parameters. The number of intra-resonator passes and the time that are necessary for spontaneous-emission transformation into a stationary resonance field of specified optical quality have been estimated. For large unstable resonators with a Fresnel number of 100 to 200 and a geometric magnification factor of 1.5 to 2, the formation time of a resonance beam with a Strehl ratio of 0.8 is about 90 to 170 ns.

Surface electromagnetic waves (SEWs) on imperfect conductors proposed by A. Sommerfeld and J. Zenneck in the early 20th century have remained unrecognized by academic science for almost a hundred years due to a regrettable misunderstanding of theorists and unsolved radio communication problems. Recognition could have come much earlier if radiophysicists had been able to apply excitation of SEWs in the centimeter range of microwaves, generation of which became possible in the first half of the 20th century with development of radar. Radiophysical experiments on excitation of surface electromagnetic waves on conductors in the centimeter range of radio waves are presented. A method for selective excitation of SEWs is described. Its essence is that the space radio wave radiation is suppressed by screening while the SEW on the conductive strip is excited by isolated currents launched through a slit in the screen.

The recently published experimental data on the acoustic monitoring of the impact of a train of picosecond laser pulses with a total duration of about 500 ns and energy density up to 2 J cm⁻² on a metal have been analyzed. During monitoring, the behavior of the acoustic signal delay τ_n with respect to the laser signal has been recorded. A comparison of the average acoustic delay τ₀ for successive laser trains directed to the same target point (with a train-to-train interval of 30 s) shows a small variation in τ₀ (< 0.1 ns), which is indicative of weak effect of ablation on the behavior of τ_n during a laser train. Under the conditions of additional laser irradiation in the intervals between trains, acoustic delay measurements demonstrate an increase in the average delay τ0 for subsequent trains, which may be related to the metal surface ablation caused by the additional irradiation.

In this work, we study a two-dimensional problem in thermoelasticity for a half-space with microstructure whose surface is subjected to a uniform thermal shock. The problem is solved in the context of the theory of generalized thermoelasticity with dual phase lags. The equations of the linear theory are also studied by the normal mode technique. The results of micropolar generalized thermoelasticity and generalized thermoelasticity are deduced as special cases from the present formulation. The Mathematica package is used to illustrate the analytical results for numerical values of the temperature, displacement, the force stress component, and the tangential couple stress; and results are depicted in different figures. A detailed analysis of the effects of phase lags and microstructure on field variables is presented on the basis of analytical and numerical results, and significant points are highlighted.

The effect of static electric field on a nematic cell with side electrodes in the transition state (which occurs in the initial stage of field effect on the cell) has been investigated within the two-dimensional dynamic model. The dynamic model is compared with the previously used static one. The two-dimensional dynamic model is found to yield better agreement with the experiment.

The resolution of interferometric method of a sound source localization is analyzed. Two realizations of this method are presented, which do not call for the knowledge of the propagation medium characteristics for determining the source coordinates. These realizations solve the problem of identifying a low-noise source in water areas where acoustic calibration cannot be performed. The maximum applicability range of the method is estimated; this estimate makes it possible to optimize the source signal processing.