Vol 165, No 1 (2024)

The results of studies of isotope-selective laser infrared (IR) multiphoton dissociation (MPD) of ¹¹BCl₃ molecules in a natural mixture with ¹⁰BCl₃ by the radiation from a pulsed CO₂ laser in the case of their irradiation with a sensitizer – SF₆ molecules, which are simultaneously acceptors of radicals – Cl atoms formed during dissociation of BCl₃ molecules are presented. A strong increase in the efficiency of dissociation of ¹¹BCl₃ molecules was discovered when they were irradiated with SF₆ molecules compared to the case of irra- diation without SF₆. The main parameters of isotope-selective IR multiphoton dissociation of BCl₃ molecules were measured – the dissociation yields of 11BCl3 (β₁₁) and 10BCl₃ (β₁₀), as well as the selectivity of dissociation of ¹¹BCl₃ molecules relative to 10BCl₃ molecules (α(¹¹B/¹⁰B)). The dependences of these parameters on the pressures of the irradiated gases BCl₃ and SF₆, as well as on the energy density and frequency of the exciting laser radiation were obtained. The main products formed upon irradiation of the mixture of BCl₃ and SF₆ molecules used – SF₅Cl, BCl₂F, BClF₂ and BF₃ – have been identified. A significant (several times) increase in the yield and selectivity of dissociation of ¹¹BCl₃ molecules was observed, as well as a significant decrease in the threshold dissociation energy density when they were irradiated with SF₆ compared to the case of irradiation without SF₆. This opens up the possibility of implementing single-frequency isotope-selective laser MPD of ¹¹BCl₃ molecules in unfocused laser beams at moderate (no more than 4–5 J/cm²) excitation energy density. The results obtained are important and relevant in terms of the application of the described method for the development of laser technology for the separation of boron isotopes.

A consistent analysis of the quantum state of polarization of SPDC radiation is presented and the peculiarities of the quantum state of polarization of SPDC in biaxial nonlinear optical crystals are considered. It is shown that the SPDC polarization deviation angle can exceed 15°, and the angle between the signal and idler wave vectors D can exceed 30°. Estimates of the curvature of the cone formed by SPDC radiation in biaxial crystals are also given. The influence of SPDC polarization deviation in a non-collinear mode on the entanglement of biphoton states generated by a double-crystal scheme is analyzed, it is shown that Tangle of the generated quantum state can deteriorate by 6%, and conditions are identified under which entanglement can be completely restored.

Kinetic model for composition formation in the anionic sublattice of the GaP_xAs_1-x solid solution during MBE on the (001) vicinal surface from As₂ and P₂ beam is proposed. The model was based on a twodimensional layered growth mechanism according to which terraces with a reconstructed surface are successively build up in growth areas localized in step kinks. The elementary mass transfer processes in the growth areas, on the terrace surfaces and their edges were considered. The model kinetic constants were determined by comparing the calculated values of x with experimental data. The impact of the substrate temperature, growth rate, and surface misorientation angle value on the solid solution composition is explained by exchange processes in the anionic layer on the surface and edges of terraces located outside growth areas.

The problem of non-stationary vapor-liquid nucleation is solved at a constant number of particles and a fixed cooling rate. An analytical approach to solving kinetic equations is developed, which correctly takes into account both the dependence of the work of cluster formation on its size and the non-ideality of the condensing vapor. Comparison with a similar approach based on the classical model reveals qualitative differences in the results. To assess the correctness of various approaches, simulation of the process under consideration was performed using the molecular dynamics method, the results of which are in qualitative and quantitative agreement with the proposed analytical model and are in much worse agreement with other approaches. Estimates for silicon oxide nucleation indicate that the significant difference between the equation of state of condensing vapor and the ideal gas equation may be its universal property.

In the mean-field approximation, the influence of both temperature and single-ion easy-axis anisotropy on the phase states and excitation spectra of a non-Heisenberg antiferromagnet with S = 1 is studied. The temperature dependences of vector and tensor order parameters are determined both in phases with vector and tensor order parameters. The dependence of excitation spectra on temperature and anisotropy constant has been studied. It is shown that at temperatures other than zero, an additional (non-relaxation) branch of excitations arises. The temperature dependence of the phase diagram has been studied.

We examine fluctuations of vorticity excited by an external random force in two-dimensional fluid in the presence of a strong external shear flow. The problem is motivated by the analysis of big coherent vortices appearing as a consequence of the inverse energy cascade in a finite box at large Reynolds numbers. We develop the perturbation theory for calculating nonlinear corrections to correlation functions of the flow fluctuations assuming that the external force is short correlated in time. We analyze corrections to the pair correlation function of vorticity and some moments. The analysis enables one to establish validity of the perturbation theory for laboratory experiments and numerical simulations.