Cherenkov radiation is one of the central effects in relativistic electrodynamics, which lends its name to a vast class of optical phenomena in which a moving source emits off-axis radiation, giving rise to a signature Cherenkov emission cone. When a radiation source is confined to a finite path, however, translational symmetry of its motion is removed, giving rise to edge effects that modify the canonical picture of conical emission. Here, we focus on one class of such edge effects as the key to understanding the properties of secondary radiation by laser-induced filaments. Charge-current transients near the edges of laser filaments are shown to couple Cherenkov emission to bremsstrahlung and transition radiation, giving rise to filament-length-sensitive features in the radiation field structure. We present a unified description of this class of radiation phenomena with a continuous analytical crossover from the subluminal to the superluminal setting of radiating currents and with the low-frequency cutoff in the radiation spectrum defined by the filament length.

• Received 12 April 2021
• Revised 4 July 2021
• Accepted 16 July 2021

DOI:https://doi.org/10.1103/PhysRevA.104.043509