Enhanced terahertz wave emission from air-plasma tailored by abruptly autofocusing laser beams

Abstract

Developing coherent intense broadband light sources is undoubtedly one of the key elements in pushing the frontiers of optical sciences, especially those of nonlinear terahertz (THz) optics. Plasma-based THz emitters excel in many aspects thanks to their broad radiation bandwidth, high output pulse energy and immunity to high power damage. Various excitation wavelengths and gases have been explored in the search for a stronger THz wave emission from laser-induced plasmas, whereas few attempts have been made with artificially modulated exotic wavepackets. Here we demonstrate that abruptly autofocusing-beam-induced air-plasma can give a 5.3-times enhanced THz wave pulse energy compared to normal Gaussian-beam-induced plasma under the same conditions. We believe this work will inspire a new direction for controlling THz radiation from laser-induced plasma using tools such as spatial light modulators to sculpt the excitation beams, and pave the way to THz remote spectroscopy, which is considered critical for both homeland security and environmental monitoring.