Fundamental gain suppression mechanisms in a continuous wave hydrogen fluoride overtone laser

Abstract

When lasing occurs on the overtone, a rotational nonequilibrium computer model showed that the fundamental gains are determined by three independent mechanisms. First, overtone lasing decreases the gains of the P\ (7) and PiC/) lines whose upper or lower levels are directly involved in PioC/) overtone lasing. Second, overtone lasing reduces the rate at which the low/ v = 2 states are populated by rotational relaxation and increases the rate at which the low J v = 0 states are populated by rotational relaxation, resulting in suppression of the low J fundamental gains whose upper or lower levels are not directly involved in overtone lasing. Third, overtone lasing reduces the rate at which the HF(0, /) and HF(1, J) states are populated by the various collisional deactivation processes. The computer model gave reasonable agreement with the measured fundamental zero power gain profiles, Fabry-Perot power, and spectra. The model overpredicted the fundamental gain suppression (Aa) for the P\ (8,9) and P2(8,9) lines whose upper or lower levels were directly involved in overtone lasing and underpredicted the suppression for lines PI (4) and PI (4, 5). The model predicted the suppression for lines PI (5-7) and P2(6,7) reasonably well. When the rotational relaxation rate was increased by a factor of 10, the model was in reasonable agreement with the measured suppression, A a, of all P\ (4-9) and P2(4-9) lines. However, with the increased rotational relaxation rate, the model's prediction of the experimental zero power gain and residual fundamental gain profiles was not adequate.