Intensity-surged and Bandwidth-extended Terahertz Radiation in Two-foci Cascading Plasmas

TL;DR

This paper introduces a novel method for enhancing terahertz radiation in two-color plasma generation by spatially separating the laser foci, resulting in significantly increased efficiency and bandwidth.

Contribution

The study reveals that separating the two-color laser foci along the propagation axis boosts THz generation efficiency and bandwidth, challenging the conventional overlap approach.

Findings

THz conversion efficiency increased by an order of magnitude.

Bandwidth of THz radiation more than doubled.

Achieved >100 THz bandwidth with 800/400 nm lasers.

Abstract

The two-color strong-field mixing in gas medium is a widely-used approach to generate bright broadband terahertz (THz) radiation. Here, we present a new and counterintuitive method to promote THz performance in two-color scheme. Beyond our knowledge that the maximum THz generation occurs with two-color foci overlapped, we found that, when the foci of two-color beams are noticeably separated along the propagation axis resulting in cascading plasmas, the THz conversion efficiency is surged by one order of magnitude and the bandwidth is stretched by more than 2 times, achieving $10^{-3}$ conversion efficiency and $>$100 THz bandwidth under the condition of 800/400 nm, $\sim$35 fs driving lasers. With the help of the pulse propagation equation and photocurrent model, the observations can be partially understood by the compromise between THz generation and absorption due to the spatial redistribution of laser energy in cascading plasmas. Present method can be extended to mid-infrared driving laser, and the new records of THz peak power and conversion efficiency are expected.