Ionization currents and terahertz emission from the interaction of few-cycle laser pulses with gas targets

Abstract

Based on a theoretical model and numerical simulations, the ionization currents and subsequent terahertz (THz) emission induced by the interaction of a few-cycle laser pulses with He gas targets are studied. It is shown that owing to the large transverse current generated by field ionization with few-cycle laser pulses, strong THz emission can be generated. The change of the carrier phase of the few-cycle laser pulses leads to the variation of the ionization currents. Correspondingly, the THz emission amplitude shows the characteristic as a periodic function of the carrier phase, which is also confirmed by one-dimensional particle-in-cell simulations. For a given carrier phase, the THz emission amplitude is not proportional to the laser amplitude. It shows at least two peaks at certain laser amplitudes. When the gas density profile is not uniform, the emission amplitude has a similar dependence on laser amplitude and carrier envelope phase, but the THz pulse duration and spectrum are quite different.

THz wave emission from argon in two-color laser field

“…[1][2][3][4] There are a large number of theoretical approaches to account for the THz emission. The fundamental mechanism is described as the "fourwave mixing" (FWM) [5] and the transient plasma current [6][7][8][9] process. When a fundamental and a second harmonic laser field are mixed, the explanation is usually on the basis of the transient plasma current process in plasma [9][10][11][12][13][14][15][16][17] and semiconductor, [18][19][20][21][22] where the THz emissions are due to the subsequent electron dynamics following ionization induced by the incident laser field in the matter.…”