Electron density wave and generation of ultrashort pulses in a high-pressure CO2 amplifier

A theoretical analysis is made of the mutual influence of a high-power CO₂ laser radiation pulse propagating in a gaseous medium and an electron density wave originating from this pulse. It is shown, in terms of a simplified model for ionization by electron collisions, that this influence can lead to a substantial shortening of nanosecond and picosecond pulses. Two mechanisms contribute to this process: an active mechanism involving absorption of the radiation energy by the electrons and a reactive mechanism for which compensation of the phase modulation caused by the electron density wave is necessary. The efficiencies of these mechanisms depend in different ways on the gas pressure. It is shown that there is an optimal pressure at which the pulse duration is the shortest.