A novel computer model of a pulsed H2/SF6 nonchain first vibrational overtone HF chemical laser has been constructed to investigate the competition between the overtone and fundamental laser performances. This model including the rotational relaxation process, can simultaneously simulate both fundamental and overtone lasing processes since undesirable fundamental lasing cannot completely be suppressed during experimental overtone oscillation. The relationship between resonator conditions and laser gains was studied. A He diluent gas up to 400 Torr is added to the basic gas mixture H 2/SF6=12.5/87.5 (Torr) in order to suppress the fundamental small signal gain. Under this gas mixture the overtone output energy of 117 mJ/l can be obtained, which is reduced to 63% compared with the one without diluent gas. The overtone output energy is found to be very sensitive to the residual reflectivity of the mirrors over the fundamental lasing band.
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