Observation of instabilities in hot-band oscillation of a CO_2 laser with a saturable absorber

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Abstract
We have observed chaotic and periodic passive Q-switching pulsations, for the first time to our knowledge, in an 11-μm hot-band oscillation of a CO2 laser, using SF6 and CCl2 F2 as intracavity saturable absorbers. The observed pulse shapes are well reproduced by the calculation based on a novel rate-equation model with consideration of vibration–vibration energy-transfer processes between highly excited vibrational levels in the CO2 laser medium. The passive Q-switching dynamics is found to be strongly correlated with the relaxation of the lower laser level. The vibrational relaxation rate constant is estimated by the analysis of pulse shapes.