Coherent amplification of light pulses in media with a discrete spectrum

A theoretical investigation is reported of the amplification of picosecond infrared radiation pulses in a CO₂ amplifier where the gas pressure varies from 1 to 10 atm. The discrete structure of the vibrational–rotational spectrum of the CO₂ molecule gives rise to a number of special physical features of the amplification process. In the linear amplification regime a fairly short input pulse creates a train of pulses which follow one another and the period is governed by the discrete nature of the spectrum of the amplifying medium. In the nonlinear regime only the first pulse of a train is amplified effectively. A train of this kind does not appear when the duration of an input pulse is greater than the reciprocal of the frequency width of the spectrum of the medium. Instead, strong broadening of a pulse accompanies amplification during the inital stage of the process and this may be used to generate synchronized picosecond and nanosecond pulses.