Numerical study of the efficiency of a CO-laser oscillation on overtone or fundamental transitions depending on the lasing spectrum width

A numerical model taking into account the multiquantum vibrational–vibrational exchange processes is developed for simulating a CO laser on a CO–N₂ mixture. The energy characteristics of a CO laser operating either on overtone or fundamental transitions, depending on the number of vibrational–rotational transitions falling within the band of a selective resonator, are studied theoretically. Particular emphasis is placed on forecasting the efficiency of narrow-band lasing (on one, three, and five transitions) depending on the position of the centre of the filter's spectral window and the resonator Q factor. It is shown that using the approximation of the single-quantum vibrational–vibrational exchange introduces a considerable error in the calculation of the characteristics of a CO laser with a narrow-band filter (1–5 transitions). The law of the increase in the lasing energy with increasing the spectral-filter bandwidth (from one to 35 transitions), the centre frequency of which corresponds to the 23→22 and 24→22 transitions for the fundamental and overtone bands, respectively, is studied. It is shown that, even for lasing on five neighbouring transitions, the output energy exceeds 50% of the energy achieved in the free-running mode.