Analytical description of generation of the residual current density in the plasma produced by a few-cycle laser pulse

Abstract

When a gas is ionized by a few-cycle laser pulse, some residual current density (RCD) of free electrons remains in the produced plasma after the passage of the laser pulse. This quasi-dc RCD is an initial impetus to plasma polarization and excitation of the plasma oscillations which can radiate terahertz (THz) waves. In this work, the analytical model for calculation of RCD excited by a fewcycle laser pulse is developed for the first time. The dependences of the RCD on the carrierenvelope phase (CEP), wavelength, duration, and intensity of the laser pulse are derived. It is shown that maximum RCD corresponding to optimal CEP increases with the laser pulse wavelength, which indicates the prospects of using mid-infrared few-cycle laser pulses in the schemes of generation of high-power THz pulses. Analytical formulas for optimal pulse intensity and maximum efficiency of excitation of the RCD are obtained. Basing on numerical solution of the 3D time-dependent Schr€ odinger equation for hydrogen atoms, RCD dependence on CEP is calculated in a wide range of wavelengths. High accuracy of analytical formulas is demonstrated at the laser pulse parameters which correspond to the tunneling regime of ionization. V C 2015 AIP Publishing LLC. [http://dx.

High Harmonic Generation from Oriented Asymmetric Molecules in the Presence of Static Electric Field

“…The three-dimensional TDSE ( 3) is solved in the cylindrical coordinate system using the splitstep method with fast Fourier transform along the longitudinal direction, and discrete Hankel transform along transverse direction [10,11]. We use the numerical grid with the transverse size of 60 and the longitudinal size of 410.…”

Quantum-mechanical simulations of low-frequency current excitation during ionization of many-electron atoms by intense laser pulses

“…These include the excitation of a lowfrequency current (with frequencies much lower than the optical one) in a plasma created by a laser pulse. The interest to this phenomenon is associated with the possibility of its use for the generation of coherent and broadband radiation in the terahertz and midinfrared ranges and possibility of tuning the spectrum of generated radiation [1][2][3][4][5][6][7][8][9][10][11]. The low-frequency current density is excited effitiently under the asymmetry of ionizing pulses [1][2][3][4][5][6][7][8][9][10] or ionized molecules [11].…”

“…The interest to this phenomenon is associated with the possibility of its use for the generation of coherent and broadband radiation in the terahertz and midinfrared ranges and possibility of tuning the spectrum of generated radiation [1][2][3][4][5][6][7][8][9][10][11]. The low-frequency current density is excited effitiently under the asymmetry of ionizing pulses [1][2][3][4][5][6][7][8][9][10] or ionized molecules [11]. Among the various methods of generating low-frequency current, the most wellknown one is based on the use of two-color ionizing laser pulses [1][2][3][4][5][6][7][8].…”

“…The efficient excitation of high-power terahertz and mid-infrared radiation is associated with the need to use of high-intensity laser pulses, which produce fast ionization of a gas medium and accelerate the freed electrons up to high energies [2,5,7,9,10]. The action of such intense pulses on atoms or molecules (most of which are multielectron quantum systems) may be accompanied by a dynamic response of various electron orbitals, which was not taken into account in previous similar studies.…”

Quantum-Mechanical Description of Ionization-Induced Generation of Tunable Mid-Infrared Pulses

“…The quantum-mechanical approach is based on the solution of the threedimensional time-dependent Schrödinger equation for the electron wave function [9,11]. The range of applicability of the semiclassical approach is limited by the laser pulse parameters corresponding to the tunneling ionization regime, at which the Keldysh parameter γ = I p /2U p [12] is much less than unity (here I p is the ionization potential of an atom, and U p is the ponderomotive energy of an electron in the laser field) [5,11,13]. For γ ≫ 1, the electron release occurs at a time of the order of the field period and greater, and to adequately calculate the low-frequency current density it is necessary to apply the quantum-mechanical approach.…”