Bright single-cycle terahertz source based on gas cells irradiated by two-color laser pulses

TL;DR

This paper demonstrates a novel method for generating bright, single-cycle terahertz radiation using gas cells irradiated by intense two-color femtosecond laser pulses, leveraging plasma oscillations and strong electric fields.

Contribution

It introduces a new approach to produce efficient, single-cycle terahertz pulses via plasma oscillations in small gas cells driven by two-color laser pulses.

Findings

Efficient conversion of electron energy into terahertz radiation.

Existence of strong quasi-static electric fields during plasma oscillations.

Homogeneous plasma oscillations in sub-20μm gas cells.

Abstract

We study the excitation of electron currents in a transparent cell of sub-millimeter size filled by an atomic gas and illuminated by an intense two-color femtosecond laser pulse. The pulse consists of a strong fundamental component and its second harmonic of low intensity, both circularly polarized. We show that for sufficiently small $20\mu$m cells the plasma oscillation excited by asymmetric ionization is almost spatially homogeneous within the interaction volume. This coherent dipole plasma oscillation results in a remarkably efficient conversion of the electron energy into that of radiation emitted in the terahertz frequency domain. Simultaneously, strong quasi-static electric fields of maximal strength $E_m\simeq 10$MV/cm are shown to exist inside the cell during several hundred femtoseconds after the ionizing two-color laser pulse has gone.