In this paper we discuss the ultrafast transfer of charge and energy in a metal in the kinetic approximation. An exact solution of the Boltzmann transport equation for the electron distribution ...function in the relaxation time approximation is obtained, which is used to calculate transport coefficients for charge and heat fluxes. Different regimes of energy transfer under conditions of significant spatial dispersion and non-equilibrity of the electron distribution function are discussed.
•Ultrafast transfer of charge and energy in a metal is considered.•Boltzmann transport equation solved for electrons on small time scales.•Analytical solution for the energy flux density in metals is obtained.•Energy transport is suppressed by the nonlocality.
•Two-temperature model is not applicable when electrons are far from the equilibrium.•Boltzmann transport equation can be used instead of the two-temperature model.•Heat transfer is different when ...electrons are not thermal.•Electron-phonon relaxation affects heat transfer.
In the current report we investigate the processes of heat transport and energy relaxation in metals using Boltzmann transport equation for the electron distribution function perturbation, simultaneously accounting both energy and momentum relaxation. Mutual influence of electron-electron and electron-phonon energy relaxation on the electron distribution function is considered using linearized integro-differential collision integrals. These energy exchange effects provide main contribution to the difference between results obtained using Boltzmann equation solution and widely considered two-temperature model.
The generation of low-frequency quasi-cylindrical and surface waves generated by a long pulse of laser radiation focused into a narrow strip on the metal surface is studied. Waves are generated by ...non-linear currents arising from inhomogeneous heating of electrons. It is shown that the total low-frequency field is mainly determined by the quasi-cylindrical wave field. The angular and frequency distributions of the generated radiation energy have been studied. The range of angles in which it is necessary to take into account the near-surface structure of quasi-cylindrical waves is established.
•Terahertz field generation in a case of a long laser pulse effect is studied.•Contribution from the quasi-cylindrical wave is dominant at any distance.•Inhomogeneous heating of electrons is the main mechanism of generation.
•Current-voltage characteristic of the radiating Josephson sandwich is obtained.•It makes possible to establish the dependence of the generation frequency on current.•It is shown that as the current ...increases, the frequency of generation stabilizes.•That property is attractive for the creation of generators on the base of Josephson vortices.
Josephson sandwich is considered, along which the radiating chain of vortices travels. Uniform movement of the chain is supported by bias current. The current-voltage characteristic connecting this current with the voltage at the Josephson junction is found. It is shown that when the current increases, generation of electromagnetic waves with frequency weakly dependent on the current is possible.
The action of an s-polarised femtosecond laser pulse is found to result in nonlinear currents in a metal film, which arise due to the nonuniform heating of the conduction electrons and under the ...influence of the drag force. The Fourier transforms of a low-frequency magnetic field generated by nonlinear currents are calculated. It is shown that when the film thickness is less than the scale of the low-frequency field nonuniformity, the amplitude of the terahertz signal increases in inverse proportion to the film thickness. If the thickness of the film is less than the depth of the skin layer at the laser frequency, the low-frequency signal is amplified inversely proportional to the square of the film thickness.
The absorption of radiation by inhomogeneous plasma formed during multiphoton ionization of inert gas atoms has been studied. We considered conditions under which the incident radiation frequency is ...close to the plasma frequency in the depth of the plasma, where the photoelectron density is constant. Under these conditions, due to the expansion of the field penetration region into the plasma, the absorption coefficient increases significantly. The dependence of the absorption coefficient on the effective frequency of photoelectrons collisions with neutral atoms and on the thickness of the layer in which the photoelectron density grows linearly was found.
Abstract
The generation of terahertz (THz) radiation in a doped semiconductor with a sufficiently large bandgap interacting with a femtosecond pulse of IR range has been investigated. Generation ...occurs due to the simultaneous effect on the conduction electrons of a constant magnetic field and time-dependent ponderomotive force. The spectral composition, total energy and shape of the THz radiation pulse are found.
Abstract
The intensities of two types of Cherenkov waves arising at the motion of a solitary vortex along a Josephson sandwich are compared. These waves arise in the tail part of the vortex or are ...emitted deep into the medium surrounding the sandwich. The vortex velocities at which one of these two types of waves excited by the Cherenkov mechanism dominates are determined.
We consider the problem of trajectory optimization by a switchable system whose continuous motion is described by differential equations; and discrete state changes (switching), by recurrent ...inclusions. Its motion is continuously controlled by choosing the state of the discrete part of the system. The number of switchings and time of switching are not predefined. The quality of the trajectory is characterized by a functional that takes into account the costs of each switch. Together with the task of optimizing the trajectories of motion, the task of finding the minimum number of switchings at which the value of the quality functional does not exceed the given value is solved.
