Spectral self-action of THz emission from ionizing two-color laser pulses in gases

TL;DR

This paper investigates how THz emission from ionizing two-color laser pulses in gases interacts with free electrons, leading to spectral broadening and nonlocal effects, with implications for THz generation efficiency.

Contribution

It introduces a semi-analytic model and simulations revealing the self-action mechanism of THz emission and its impact on spectral broadening in gases.

Findings

THz signals interact with free electrons, affecting subsequent THz generation

Spectral broadening is primarily due to self-action effects

Diffraction limits the THz bandwidth by depleting low frequencies

Abstract

The spectrum of terahertz (THz) emission in gases via ionizing two-color femtosecond pulses is analyzed by means of a semi-analytic model and finite-difference-time-domain simulations in 1D and 2D geometries. We show that produced THz signals interact with free electron trajectories and thus influence significantly further THz generation upon propagation, i.e., make the process inherently nonlocal. This self-action plays a key role in the observed strong spectral broadening of the generated THz field. Diffraction limits the achievable THz bandwidth by efficiently depleting the low frequency amplitudes in the propagating field.