FUNDAMENTAL GAIN SUPPRESSION MECHANISMS IN A CONTINUOUS-WAVE HYDROGEN-FLUORIDE OVERTONE LASER

When lasing occurs on the overtone, a rotational nonequilibrium comput er model showed that the fundamental gains are determined by three ind ependent mechanisms, First, overtone lasing decreases the gains of the P-1(J) and P-2(J) lines whose upper or lower levels are directly invo lved in P-20(J) overtone lasing. Second, overtone lasing reduces the r ate at which the low J nu = 2 states are populated by rotational relax ation and increases the rate at which the low J nu = 0 states are popu lated by rotational relaxation, resulting in suppression of the low J fundamental gains whose upper or lower levels are not directly involve d in overtone lasing. Third, overtone lasing reduces the rate at which the HF(0, J) and HF(1, J) states are populated by the various collisi onal deactivation processes. The computer model gave reasonable agreem ent with the measured fundamental zero power gain profiles, Fabry-Pero t power, and spectra. The model overpredicted the fundamental gain sup pression (Delta alpha) for the P-1(8, 9) and P-2(8, 9) lines whose upp er or lower levels were directly involved in overtone lasing and under predicted the suppression for lines P-1(4) and P-2(4, 5). The model pr edicted the suppression for lines P-1(5-7) and P-2(6, 7) reasonably we ll. When the rotational relaxation rate was increased by a factor of 1 0, the model was in reasonable agreement with the measured suppression , Delta alpha, of all P-1(4-9) and P-2(4-9) lines. However, with the i ncreased rotational relaxation rate, the model's prediction of the exp erimental zero power gain and residual fundamental gain profiles was n ot adequate.