Radiophysics and Quantum Electronics最新文献

We propose an original method for stretching narrow-band laser pulses by installing a chirped volume Bragg grating in the resonator cavity of a regenerative amplifier. Stretching of pulses with a bandwidth of 0.1 nm to a duration of more than 2 ns with a simultaneous increase in the pulse energy by four orders of magnitude and the formation of a nearly rectangular time profile of the pulse is demonstrated experimentally.

We consider the possibility of creating a compact source of extreme ultraviolet radiation, which is based on a free-electron laser using a microundulator with a period of 1 mm and a plasma accelerator with a wake wave. It is shown that the use of a microundulator allows one to significantly reduce the length of the interaction space and increase the resistance of the free-electron laser to the angular spread of the beam particles as compared to a longer-period undulator. Analytical estimates of the growth rate of the radiation power and the sensitivity to the spread of the beam parameters agree well with the results of numerical simulations using the Genesis 1.3 code. The feasibility of a pulsed microundulator having the required parameters is demonstrated experimentally.

In ultra-high-power laser systems, actively developed in recent years, one of the tasks is to ensure homogeneity in the transverse intensity distribution of the laser beam. Inhomogeneities caused by optical defects give rise to “hot spots,” which considerably limit the pulse energy of such systems. A promising method for addressing this issue is the use of asymmetric chirped-pulse compressors. This article reports experimental results on smoothing spatial fluence modulation in laser beams within asymmetric planar and nonplanar chirped-pulse compressors.

We present a four-channel prototype of a system for spatial convergence and coherent addition of tightly focused femtosecond laser beams in counter-propagating geometry. During the interference of the individual laser channels in the main focus of the system a standing laser field configuration close in its structure to the dipole focusing underlying the design of the exawatt XCELS project is realized. The prototype uses radiation from a pulsed femtosecond laser source operating at a repetition rate of about 80 MHz without additional amplification inside the laser circuit. A two-stage system for stabilizing the laser radiation direction at the input to the convergence circuit, as well as the phase stabilizing system for four beams are developed and tested.

We consider the dependence of the conditions of electron runaway in the gas gap on the degree of inhomogeneity of the electric field distribution, which is regulated by using conical cathodes with different opening angles. It is shown that for cones with large angles (weakly inhomogeneous field), the runaway condition is similar to the condition for a uniform field, i.e., the field strength near the cathode must exceed a critical value, which depends on the type of gas and its density. For cones with small angles (strongly inhomogeneous field), this condition is not sufficient: an electron that runs away near the cathode can become a thermal one in a weak field at the periphery. Then for electrons to run away, it is necessary that the voltage applied to the gap exceeds a certain threshold, depending both on the properties of the gas and on the gap width.

We find the conditions, under which a gyroresonance traveling wave tube (gyro-TWT), which is based on a helical corrugated waveguide can operate as a nonlinear element having a strong dependence of the phase shift on the input signal amplitude. It is shown that the use of such an element in the feedback circuit of another gyro-TWT operating as a high-efficiency amplifier allows one to obtain chaotic broadband generation with low spectrum nonuniformity. The parameters of a millimeter-wave generator having an output power of more than 80 kW, a relative spectrum width of about 10%, and a total efficiency of about 9% are calculated.

We analyze the excitation of electromagnetic waves of the extremely low frequency (ELF) range by an ionospheric distributed ring current induced in the ionospheric F region by high-power modulated HF wave radiation of the heater. Analytical expressions are obtained for the components of electric and magnetic fields within the framework of a simple layered model of the ionosphere. The spatial structure of the fields in the ionosphere and the Earth–ionosphere waveguide is calculated. Dependences of the magnetic field components on distance to the source and altitude in the ionosphere are studied. Frequency dependence of the field is analyzed.

We present the results of measuring intensity variations of atmospheric emission in the 630, 557.7, and 391.4 nm lines, caused by the impact of high-power short-wave radio emission of the Sura heating facility on the ionosphere. The data were obtained using a three-channel photometer located in the immediate vicinity of the heater. In the experiments of 2023 and 2024, a regular increase in the emission intensity in the 391.4 and 557.7 nm lines, induced by the Sura radiation, was recorded for the first time.

We examine the role of nonlinear aspects of the Compton effect in the development of narrow-band gamma-ray sources based on the interaction between electron beams and laser pulses. The study focuses on parameters relevant to the ongoing project at the National Center for Physics and Mathematics (NCPM). We present estimates of photon yield and relative spectral width, along with an assessment of how laser and electron beam parameters influence these characteristics. The study primarily focuses on the weakly nonlinear regime of the Compton effect, where light pressure on electrons is significant but not dominant, and quantum effects are negligible. We employ both analytical calculations and numerical modeling to describe gamma-ray generation processes and to optimize system parameters. The potential for investigating the strongly nonlinear regime within the framework of this project is also discussed. The results obtained contribute to the development of highly efficient narrow-band gamma-ray sources.

We perform a comparative study of the techniques for spatial processing of partially coherent signals with discrete spatial spectrum, which are received by a large antenna array in a randomly inhomogeneous multimode waveguide. The array gain in conventional terms of the signal-tonoise-plus-interference ratio is used as a criterion of the processing effectiveness. Our main attention has been paid to consideration of heuristically motivated suboptimal array processors, which, unlike the optimal processors, do not require complete information about the coherence functions (matrices) the useful signal and the interference at the array input. The key issue here is to estimate the range of the problem parameters where suboptimal processors turn out to be the most effective with an appropriate choice of their implementation parameters. Numerical calculations are carried out on the basis of a previously developed physical model of the partially coherent multimode signals, which corresponds to their formation at the input of a horizontal acoustic array arranged in a shallow-water acoustic channel (for a channel from typical of the Barents Sea in the summer season). It is shown that in the most complicated scenario where a relatively weak and coherence-degraded multimode signal is received against the background of intense multimode interference under conditions of a significant overlapping of their spatial (modal) spectra, the array gain for the proposed suboptimal techniques can reach values close to the maximum possible ones and significantly exceed the gain level determined by the total number of receiving-array elements.