Production of extended plasma channels in atmospheric air by amplitude-modulated UV radiation of GARPUN-MTW Ti : sapphire — KrF laser. Part 1. Regenerative amplification of subpicosecond pulses in a wide-aperture electron beam pumped KrF amplifier

Regenerative amplification of single and multiple ultrashort subpicosecond UV pulses in a wide-aperture KrF amplifier with an unstable confocal resonator was investigated on the GARPUN-MTW hybrid laser system. Amplitude-modulated 100-ns long UV radiation pulses with an energy of several tens of joules were obtained at the output of the system. The pulses were a combination of a quasi-stationary oscillation pulse and a train of amplified ultrashort pulses (USPs) with a peak power of 0.2 — 0.3 TW, which exceeded the power of free-running lasing pulse by three orders of magnitude. The population inversion recovery time in the active KrF laser medium was estimated: τ_c ≤ 2.0 ns. Trains of USPs spaced at an interval Δt ≈ τ_c were shown to exhibit the highest amplification efficiency. The production of amplitude-modulated UV pulses opens up the way to the production and maintenance of extended plasma channels in atmospheric air.