Steering laser-produced THz radiation in air with superluminal ionization fronts

TL;DR

This paper shows how to steer laser-produced THz radiation in air at large angles or backwards by controlling the ionization front speed using the flying focus technique, enabling remote THz spectroscopy.

Contribution

It introduces a method to steer THz radiation in air by adjusting the ionization front speed with the flying focus technique, a novel approach for remote THz applications.

Findings

THz radiation can be directed at large angles or backwards.

The steering is achieved by controlling the ionization front speed.

The method enables remote THz spectroscopy applications.

Abstract

We demonstrate that pulsed THz radiation produced in air by a focused ultrashort laser pulse can be steered to large angles or even in the backward direction with respect to the laser propagation axis. The emission angle is adjusted by the flying focus technique, which determines the speed and direction of the ionization front created by the single-color laser pulse. This easily adjustable THz source, being well separated from the intense laser, opens exciting applications for remote THz spectroscopy.