Bulletin of the Lebedev Physics Institute最新文献

We consider the interaction of a short, relativistically intense laser pulse with (sub)micron dense plasma bunches of various shapes. The electromagnetic field scattered by such targets is shown to consist of a sequence of ultrashort, tightly focused attosecond pulses. The spatial characteristics and temporal duration of such pulses are estimated and numerically calculated as functions of the parameters of the target and the laser pulse.

We discuss the generation of nonlinear harmonics by an intense dipole electromagnetic pulse in a vacuum in the presence of a constant magnetic field. Using Maxwell’s nonlinear equations, following from the Heisenberg–Euler Lagrangian in the one-loop approximation, expressions are derived for the electromagnetic field of the second harmonic generated in this case. It is shown that the second harmonic pulse in its spatial structure is a magnetic octupole pulse if the initial electromagnetic pulse is an electric- or magnetic-dipole pulse.

We report an investigation of the process of Compton scattering of a plane-wave laser pulse on an electron in the nonlinear regime in the head-on collision geometry. Use is made of the generalized Filon method to calculate numerically the rapidly oscillating integrals that determine the matrix element of the process in the Furry representation. The behavior of the spectral-angular, angular, and spectral distributions of a scattered photon is analyzed as a function of the laser pulse amplitude, duration, polarization, and envelope shape. A new analytical expression for the backscattering spectrum is obtained for a special envelope shape of a circularly polarized pulse.

We study the methods for modifying and microstructuring polyvinylidene fluoride (PVDF) films using nanosecond and femtosecond laser pulses in order to form functional microstructures on the surface and in the near-surface layer. It is shown that microstructuring by femtosecond pulses makes it possible to ensure high resolution and minimal thermal impact on the material. The advantage of using nanosecond radiation is the possibility of rapid microstructuring over large areas, which makes this method attractive for industrial applications, with the resolution not reaching high values. We have found regimes that allow one to form structures in the near-surface layer without damaging the film surface, as well as to produce structures with an increased content of atomic carbon. The results of Raman spectroscopy show that in the regions of strong laser action there is a significant change in the conformational composition of the films, including a decrease in ferroactive conformations and a transition to the paraelectric state, which, in turn, affects the piezoelectric properties. The proposed methods for laser modification of PVDF films can be used to develop new microsensors, which opens up new horizons in the field of application of electroactive materials in various high-tech industries.

It is shown that for an optically inhomogeneous medium, which is a suspension of submicron-sized particles in liquid, both a noticeable increase in the time of radiation interaction with the medium and growth of the Raman scattering (RS) signal are possible compared to the medium without scatterers. The optical heterodyning method was used in experiments to measure the time delay of femtosecond pulses, which reached 1 ps in suspensions of rutile microparticles in dimethyl sulfoxide (DMSO) for different scatterer volume fraction. The photon dwell time in the suspensions decreased with with scatterer volume fraction increase for scatterer volume fraction higher than 0.001. Numerical simulation results of  femtosecond laser pulse scattering by Monte Carlo method are in good agreement with experimental data. The simulation indicates that the maximum possible growth of the Raman signal registered in the diffuse reflection direction under multiple light scattering is up to 7.5-fold compared to the case of scatterer absence in the medium. The Raman signal collected with a lens increased 3.5 times in a suspension of rutile particles in DMSO compared to the Raman signal for DMSO without scatterers. The simulation results of Raman process in a scattering medium agree well with the experimental results of Raman signal efficiency measurement.

We report and analyze various methods for reducing the angle random walk (ARW) of fiber-optic gyroscopes. The operating principle and noise theory of a fiber-optic gyroscope are briefly considered. Main attention is paid to the most popular ways to reduce ARW: increasing the total area of the fiber coil, optimizing the phase modulation depth, and reducing and compensating for the relative intensity noise (RIN). Other ways to reduce ARW are also briefly discussed, for example, by reducing the phase modulation frequency. Experimental results of applying the described methods for reducing ARW are demonstrated using advanced work on the development of fiber-optic gyroscopes as an example.

Millisecond laser sources are now widely used in assisted reproductive technologies for the trophectoderm cell biopsy procedure at the blastocyst stage. We have investigated the effectiveness of application for this purpose of infrared femtosecond laser pulses (280 fs duration and 1028 nm radiation wavelength). The biopsy was performed using standard microsurgical assist devices—holding pipettes. Pulses with an intensity of 10 to 65 TW/cm² were shown to be able to extract cells from bioptates of different thickness.

A detailed analysis of spectroscopic features and of the zonal and sectorial internal structure of a multisectorial HPHT diamond sample grown in the Fe–Ni–C system is presented. The sample was irradiated by electrons with energy of 3 MeV and a dose of 1.5 × 10¹⁸ electron cm^–2 and then annealed in vacuum at 1200°C to obtain a high concentration of nitrogen-vacancy centers. Differences are established in the concentrations and incorporation forms of nitrogen in different growth sectors and of nitrogen-vacancy defects formed as a result of the treatment. Comparison of photoluminescence (PL) spectra at excitation at 488 and 785 nm and the distribution of nitrogen defects with the results of PL visualization under radiation with wavelengths of 220, 254, and 365 nm showed that photoluminescence tomography is a very informative tool for analyzing the inhomogeneity of diamond products. The Ni impurity was localized nonuniformly, many additional PL lines in the near-IR range were registered in the zones of sector {111} with high concentration of A-defects. This feature complements the defect-impurity composition of the diamond element with a high concentration of NV centers and may adversely affect the characteristics of a promising laser material.

We report a numerical investigation of the spatiotemporal dynamics of a femtosecond laser pulse after aperture separation on a circular serrated diaphragm and a spatial filter. It is found that the use of serrated diaphragms together with a spatial filter can markedly reduce the negative impact of diffraction effects on the spatiotemporal dynamics of the pulse. Criteria are formulated to determine the parameters of the separation scheme in order to avoid significant distortions of the radiation properties during subsequent focusing.

Reduced models for combustion often are based on low-dimensional manifolds (LDMs) in state space, to which the evolution of the system is restricted. To describe the evolution of states on the manifold, an explicit parametrization of the manifold, which allows expressing the thermochemical states on the manifold by known functions of some parameter, can be useful. For technical reasons, a parametrization of a low-dimensional manifold in terms of a linear combination of species (and possibly other state variables, e.g., temperature) is desired. This linear combination is often chosen such that it allows physical interpretation in terms of a chemical progress, and is therefore termed progress variable (PV). A widespread task in the development and application of reduced combustion models is therefore to find a progress variable-based parametrization for a given low-dimensional manifold. This paper describes a lightweight, effective method for constructing (if at all possible) such a linear combination-based progress variable. Compared to other, existing methods for progress variable construction, the method is simple to implement, does not requires nonlinear optimization procedures and is therefore computationally highly efficient and robust. Application of the method to a wide range of combustion systems (ignition, flame extinction, featuring multicomponent fuels) shows its good performance and robustness.