In this work, it is shown that the dependence of the mass of conductive band electrons in a metal on their energy can be a reason of enhancement of the absorption of powerful laser radiation by the metal. To do this, a problem of response (current) of the electron placed in one-dimension periodic potential (lattice) to an electric field periodic in time (electromagnetic wave) is solved. The solution shows that for sufficiently large amplitude of the wave the dependence of the electron current on the wave amplitude becomes non-linear. Within a certain rangе of parameters, this dependence can be described by a simple formula that corresponds to the dependence of the electron mass on its energy. The formula was used for solving the problem of penetration of electromagnetic wave into a metal with the approach of modified Drude model. The non-linearity results in the enhancement of the wave absorption and generation of wave with frequencies close to those of plasma penetrating deep into the metal. The discussed effects manifest themselves in electric fields about. 1 V/Angstrom. The obtained results can be used in the interpretation of experiments data and in the creation of mathematical modeling of the interaction of powerful laser radiation with metal.

The purpose of this work is to generalize the radar method known for the inertial frame of reference to the case of a uniformly accelerated frame of reference.

The derivation of the corresponding formulas is based on the standard for the theory of relativity metric of a uniformly accelerated Möller frame of reference without applying any space-time transformation between some auxiliary inertial frame and the accelerated frame. To solve the problem of determining the trajectory of a light beam, depending on the initial direction of propagation, Fermat’s principle is used. To calculate the flight time of a photon to an object, knowing its coordinates, the condition of the light-likeness of the interval for the propagation of light is additionally introduced.

The resulting trajectory of the light particle is an arc of a circle. For a small area near the source, the photon trajectory coincides with the parabolic trajectory of a classical corpuscle. An equation has been derived for the direction in which the radio signal is sent. The actual location of the object is not in the direction of the initial motion of the photon, but somewhat lower. The value of the angle of gravitational refraction for a closely spaced resting object is calculated. The further the object is in the “horizontal” direction, the greater the angle of refraction. The flight time of the light signal to the object is found. The signal emitted in the direction that forms an acute angle with the direction of acceleration leads the radio signal in the inertial frame of reference. Therefore, for a close object located above the radiation source, the calculated Shapiro delay time is negative. The coordinates of the remote object are also calculated.

The totality of the obtained equalities completely determines the radar method. The resulting equalities, perhaps, allow for experimental verification.

The paper analyzes the evolution of the emittance of a kiloampere electron beam in a linear induction accelerator (LIA) with a discrete focusing system in order to assess the possibility of its application as a driver for generating radiation according to the free electron laser (FEL) scheme. In this analysis, special attention is paid to the geometry and parameters of the electron injector, the entry of particles from which into the accelerating structure of such an LIA mainly determines the characteristics of the beam at its exit. The features of the transverse dynamics of the beam during its passage through this accelerating structure are studied. The influence of various factors contributing to an increase in the beam emittance at the output of the LIA is considered. Analytical estimates of the beam parameters are compared with the results of numerical simulation. Based on the results of comparing the measured beam emittance with its value obtained in numerical simulation, it was concluded that the beam parameters are adequate for pumping terahertz oscillations in the FEL cavity

Detailed investigation of two-dimensional roughness element influence on the flow behind three-dimensional roughness element was carried out. For the first time studies were conducted on the windward side of the flying wing in the range of free-stream 7,2 – 20 m/s in the favourable gradient region behind roughness elements. Secondary instability mechanisms of disturbances leading to turbulence stage were investigated. It was shown that longitudinal structure forming behind three-dimensional roughness element grows downstream and has its trajectory slightly bend. The longitudinal structure consists of two stationary disturbances different in size. This can be explained by presence of cross flow and secondary disturbances leading to the transition. On the straight wing model, influence of the distributed suction on the stationary disturbance development was investigated and quantitatively determined. It was shown that suction is able to relaminarize the flow and eliminate the separation of the boundary layer.

The paper describes a digital signal processing technique for determining the relationship between disturbances in a supersonic flow and pulsations of the boundary layer of a flat plate model. Estimates of the error of the proposed data processing method are given, the results of an experiment conducted to demonstrate the method on real data are presented.

In a subsonic wind tunnel, the effect of slip and attack angles on the separation structure of the flow around the model of a trapezoidal flying wing was experimentally studied. In the course of this fundamental study, visualization patterns of a near-wall flow on the leeward side of the wing were obtained at the angles of attack of 0 and 18 degrees and oncoming flow velocity of 25 m/s. It was shown for the first time that gradual increase in slip angle of the wing leads to the restructuring of the flow, up to the disappearance of the local or global separation region on one of the consoles of the model. At the same time, on the second console, the separation is maintained. An increase in the angle of attack of the swept wing led to the development of a separation region: from a locally separated bubble to separation from the leading edge with a reverse flow and the formation of a pair of large-scale vortices. For the first time, singular points on the surface of the model for each mode have been found; by setting cone-shaped perturbation sources in these points one can achieve a significant improvement in the flow around the wing.

In the wavelength range λ = 900–1200 nm, the spectral dependences of the refractive index n and extinction coefficient κ of a thin film, which is the heterostructure based on In_0.2Ga_0.8As/GaAs quantum wells, are found. The values of n and κ found at each point of the spectrum provide the minimum of the objective function, which is the sum of the module of the differences between the calculated reflection and transmission coefficients and the measured reflection and transmission coefficients of the sample grown on the GaAs substrate.

The paper presents the results of studies of the effect of γ-irradiation on the photorefractive properties of lithium niobate (LiNbO₃), using optical absorption and Raman spectroscopy of Raman scattering. It is shown that with γ-irradiation, the optical density of the lithium niobate crystal increases, i.e. the shift of the optical absorption edge towards long waves, with an increase in the irradiation dose, the refractive index increases, in the interval 1300 ÷ 1600 cm^–1 with γ-irradiation at a frequency of 1375 cm^–1, peaks appear due to centers of significant changes in Raman scattering frequencies.