Optical-to-THz Wave Conversion via Excitation of Plasma Oscillations in the Tunneling-Ionization Process

Abstract

A new ("linear-parametric") mechanism of a direct conversion of an ultrashort laser pulse into terahertz radiation is suggested. The conversion is due to the ionization-induced excitation and the subsequent electromagnetic emission of the superluminous polarization wave created by the axicon-focused laser pulse. For a few-cycle pulse with an optimum carrier-envelope phase, the considered mechanism is found to be much more effective than the alternative one based on the excitation of plasma oscillations in the laser wakefield by the ponderomotive force and able to provide THz radiation of the gigawatt power level with the use of moderate optical intensity (approximately 10(14)-10(15) W/cm2).

Tailoring terahertz radiation by controlling tunnel photoionization events in gases

“…where γ is the phenomenological electron-ion collision rate (γ ∼ = 5 ps −1 at atmospheric pressure) and m and q are electron mass and charge [15,23,40]. In equation (1), ponderomotive forces are neglected because they play only a minor role in the situation considered here [15,20].…”

“…There are other, generally less efficient mechanisms for THz generation in gases that employ single-color pumps. Such mechanisms involve ponderomotive effects in a preformed plasma [20], excitation of plasma oscillations [21][22][23] or conical Cherenkov radiation [24][25][26].…”

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

“…The low-frequency current density excited during gas ionization by a two-color laser pulse has been previously calculated analytically and numerically with the help of semiclassical and quantum-mechanical approaches [1][2][3][4][5][6][7][8][9]. The semiclassical approach is based on the solution of the hydrodynamic equation for the electron current density and the equation for the density of free electrons with a quasi-static probability of tunneling ionization per unit time [10]. The quantum-mechanical approach is based on the solution of the threedimensional time-dependent Schrödinger equation for the electron wave function [9,11].…”

Review of Energetic Particle Generation and Electromagnetic Radiation from Intense Laser-Plasma Interactions at the Institute of Physics, Chinese Academy of Sciences

“…Both transverse and very directional forward and backward emissions have been observed. There are several different explanations for these observed emissions, such as four-wave mixing [48], ionization-induced current models [49], Cherenkov emission from the ionization front moving faster than the speed of light in the medium [50], and transition-Cherenkov emission from the plasma space 023-6 charge moving behind the ionization front [51]. Here, we study the generation of THz dipoles by tunneling and above-barrier ionization, and find that the photoelectrons perform space-charge oscillations and radiate THz waves at the local plasma frequency, depending on gas density [52].…”

“…In addition, ionizing gas targets are also potentially high-power THz sources when irradiated by laser pulses at moderate intensities such as 10 15-16 W/cm 2 [48][49][50][51]. THz emission can be produced with either one or two laser pulses.…”