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

We demonstrate that a single-color ultrashort optical pulse propagating in air can emit THz radiation along any direction with respect to its propagation axis. The emission angle can be adjusted by the flying focus technique which determines the speed and direction of the ionization front. When the ionization front velocity becomes superluminal, the THz emission corresponds to classical Cherenkov radiation.