Institute of Laser Physics

Orthorhombic strontium tetraborate is one of a few nonlinear optical materials feasible for generation of radiation in the range below 150 nm. Possibility of efficient nonlinear optical generation in strontium tetraborate depends on existence of spontaneously grown domain structures in this non-ferroelectric crystal. Present Letter reports investigation of improved domain (nonlinear photonic crystal) structure the reciprocal superlattice vector of which demonstrates increase in the vacuum ultraviolet range upon the generated wavelength decrease. Vacuum ultraviolet generation tunable from 200 to 162 nm with the efficiency above 10 –4 is achieved with the employment of starting femtosecond laser of the lowest power class.

Purpose: to fi nd the duration of hypolipidemic effect after the course of intravenous laser therapy in patients with coronary artery disease (CAD) and lipid metabolism disorders resistant to hypolipidemic pharmacotherapy. Patients and methods. 40 patients with CAD and lipid metabolism disorders (LMD) resistant to hypolipidemic drugs were enrolled in the trial. Patients were divided into two comparable groups depending on the curative technique: 20 patients from Group 1 (main group) had intravenous laser blood irradiation (ILBI) and supportive medicamentous therapy (SMT). 20 patients from Group 2 (control group) had only SMT. Results and discussion. Initially, patients in both groups had LMD signs despite of hypolipidemic drug therapy: elevated levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), atherogenic index (AI), and reduced high-density lipoprotein cholesterol (HDL-C) compared to normal values. Baseline values in both groups were statistically insignifi cant for TC, HDL-C, LDL-C and AI levels which indicated comparability between the groups. The study results demonstrated that patients in the main lasered group with ILBI course demonstrated much better hypolipidemic effect in 1 and 3 months after the treatment compared to baseline values: signifi cant reduction in TC by 19.1 % and 16.1 %, respectively; signifi cant reduction in LDL-C by 24.1 % and 21.8 %, respectively; signifi cant reduction in AI by 33.7 % and 29.1 %, respectively. Four months after the ILBI course, hypolipidemic effect became signifi cantly less evident, and lipid profi le indicators in the main group returned to baseline levels, except for total cholesterol. Therefore, in 4 months after ILBI course, patients require a repeated laser therapy course. The controls throughout the observation period had no signifi cant positive dynamics compared to baseline values. Conclusion . In patients with CAD and LMD resistant to hypolipidemic drugs, ILBI therapy corrects LMD. It has been demonstrated by the signifi cant reduction in TC, LDL-C, and AI levels, as well as by increased HDL-C level, although lipid profi le parameters did not reach their normal or target values. The obtained positive effect persisted for 3 months after the course of laser therapy. After that, ILBI positive effect gradually went down, except the total cholesterol. That is why, in four months patients require a repeat course of laser therapy. To achieve a full hypolipidemic effect in this category of patient, it is necessary to develop and incorporate other non-drug curative techniques.

This paper presents the results of an experimental study of laser generation based on electron transitions in neutral krypton atoms in the near- and mid-infrared spectral regions, pumped by a pulsed inductive longitudinal discharge of a low-pressure gas active medium. Particular attention is given to the investigation of population inversion formation conditions and experimental studies of the influence of gas mixture compositions (Kr–Ar, Kr–He, Kr–He–Ar), gas pressure, and discharge parameters on the energy, temporal, and spatial characteristics of the laser generation. For the first time, laser generation at a wavelength of 810 nm (corresponding to the 5p → 5s transition of Kr I) was recorded in a pulsed inductive longitudinal discharge at an optimal pressure of approximately 0.05 torr. Laser generation on 4d → 5p and 6s → 5p transitions (at 1442, 1476, and 2524 nm) was also detected in pure krypton at pressures around 1 torr. Temporal lasing characteristics were investigated, showing that the optical pulse duration was 6 ± 1 ns (FWHM). The spatial beam profile had an elliptical shape with dimensions of approximately 6 ± 0.2 × 5.2 ± 0.2 mm. The pulse lasing energy did not exceed 3 μJ, corresponding to a peak power of about 600 W.

This article describes a model for optimizing traffic flow control and generating traffic signal phases based on the stochastic dynamics of traffic and the percolation properties of transport networks. As input data (in SUMO), we use lane-level vehicle flow rates, treating them as random processes with unknown distributions. It is shown that the percolation threshold of the transport network can serve as a reliability criterion in a stochastic model of lane blockage and can be used to determine the control interval. To calculate the durations of permissive control signals and their sequence for different directions, vehicle queues are considered and the time required for them to reach the network’s percolation threshold is estimated. Subsequently, the lane with the largest queue (i.e., the shortest time to reach blockage) is selected, and a phase is formed for its signal control, as well as for other lanes that can be opened simultaneously. Simulation results show that when dynamic traffic signal control is used and a percolation-dynamic model for balancing road traffic is applied, lane occupancy indicators such as “congestion” decrease by 19–51% compared to a model with statically specified traffic signal phase cycles. The characteristics of flow dynamics obtained in the simulation make it possible to construct an overall control quality function and to assess, from the standpoint of traffic network management organization, an acceptable density of traffic signals and unsignalized intersections.

One of the possible optical computing methods is the use of multi-slit interference. The accuracy of various multi-slit optical experiments is difficult due to the difficulty of creating appropriate narrow slits for diffraction experiments with 2, 3 or 4 slits. The solution to these and similar technical difficulties may be to change the radiation spectrum from the classical optical range to the microwave region. This article presents preliminary two- and three-slit interference microwave test experiments. To obtain interference, various dielectric bases with metal coatings with two and three slits of different widths were used. Diffraction experiments were performed for microwave frequencies in the range from 36.3 to 53.6 GHz. The possibility of controlling microwave two- and three-slit interference by changing the polarization or introducing a time delay in the path of radiation propagation is shown. In particular, an almost complete mutual attenuation of the signal in the center of the microwave beam was obtained during interference from two slits with a phase shift of radiation from the left and right slits. The study searches for quantum effects in the near Fresnel zone and the far Fraunhofer zone. The possibility of computer simulation of wave scattering on various two-dimensional and three-dimensional objects (microwave converters) is discussed.

We have developed and tested an efficient mathematical model for calculating a coherent population trapping (CPT) resonance in a periodically modulated laser field when the modulation frequency $f$ is close to the fractional part of the hyperfine splitting frequency (HFS) in the ground state ${\mathrm{\ensuremath{\Delta}}}_{\mathrm{HFS}}/N$ (where $N=1,2,3,\dots{}$). In such a polychromatic light, only two frequency components that are most resonant with the working optical transitions in the atom are taken into account exactly, while all other off-resonant frequency components are taken into account by using the second-order perturbation theory in the field magnitude. Within the framework of our concept, an equation for the atomic density matrix is obtained, in which all off-resonant frequency components are described by two operators (which are nondiagonal in the general case): a shift operator and a relaxation operator. This model has been verified by numerical calculations for various dependencies, in which we have not found visual differences from the results of exact calculations. Thus, in our bichromatic model, the infinite variety of periodically modulated fields in CPT spectroscopy can be uniformly described by only five parameters. In addition to a significant mathematical simplification, our model provides a clear physical picture of the various features of CPT spectroscopy in a periodically modulated laser field, including some effects that have not yet been discussed in the scientific literature. In particular, we show a widespread viewpoint that the CPT resonance shift is determined by standard ac Stark shifts of the lower levels is, in general, fundamentally incorrect, since the contribution to the light shift due to beats at the frequency ${\mathrm{\ensuremath{\Delta}}}_{\mathrm{HFS}}$ between different off-resonant frequency components can be comparable to the value of standard ac Stark shift (or even dominate it). Therefore, even if we have detailed information on the spectral composition of the modulated field (e.g., using a spectrum analyzer), this is, in general, absolutely insufficient for determining the light shift of the CPT resonance.

The problem of registration of collapsing stars in the Galaxy is considered using two instruments: the optoacoustic gravitational detector OGRAN and the neutrino telescope BUST, located in the underground laboratories of the Baksan Neutrino Obstrvatory of the Institute for Nuclear Research of the Russian Academy of Sciences (BNO INR RAS). An algorithm for joint data processing on the experience of registration of the SN1987A event is presented. The proposed method is illustrated by the current output signals of these instruments.

The results of absorption modeling in the hydrogen Hα 6563 Å and helium 10830 Å lines for hot Jupiter HAT‑P-32b have been presented. The modeling has been performed using a three-dimensional hydrodynamic code together with the Monte Carlo model of Lyα photon transport. A wide range of stellar radiation and atmospheric parameters has been considered. It has been found that the measured spectrally resolved transit absorption in both lines can be well described by model calculations with the stellar radiation in the XUV range limited to 200 erg/cm2/s per 1 AU, the helium content in the planet’s atmosphere is He/H = 2/98, and metallicity is [Fe/H] = –1. It has been shown that absorption in the helium line occurs uniformly in a large volume of the outflowing atmosphere, and in the hydrogen line, it occurs in a layer of 1.5–2.75 planet radii.

The results of the experiments on modeling the processes occurring during endovenous laser coagulation (EVLC, EVLA) using laser radiation with wavelengths λ = 1.55 and 1.94 µm are presented. The application of blood plasma, which is transparent in the visible range and similar to blood in thermophysical properties and absorption coefficient at the selected wavelengths, made it possible to study these processes in detail using video filming. The experiments were carried out using fibers with end and radial radiation output, which are most often used in phlebological practice for EVLC. The results obtained on the vein model showed the following. (i) Heating of the venous wall is mainly due to convection and boiling of the liquid. When a radial fiber is used, additional heating may occur as a result of the direct action of laser irradiation due to the Moses effect. (ii) For laser radiation with λ = 1.94 µm, effective heat transfer begins at lower power levels as compared to λ = 1.55 µm. (iii) Heat transfer in EVLC occurs asymmetrically, predominantly upward. The exception is direct heating by laser radiation due to the Moses effect, which sometimes occurs when using a fiber with a radial output (iv) Periodic events of explosive boiling help to clean the radiation output area from adhered coagulate particles, which cause undesirable carbonization. The intensity of this process increases with increasing radiation power and its absorption coefficient. The results obtained may help to improve the EVLC technology.