Acoustic phenomena associated with a TEA laser discharge

Using a heterodyne technique of considerably greater sensitivity than interferometry, the authors have studied acoustic effects arising from a TEA laser discharge. Initial adiabatic expansion was observed to be followed by a slow (tens of milliseconds) diffusive relaxation process. Shock waves generated in the vicinity of the cathode and also produced by the pre-ionising arc arrays caused perturbations on a time-scale of tens of microseconds. Discharge heating of the gas caused it to expand by almost an order less than the adiabatic expansion or shock tube theories would suggest. The implications of these findings to the design of high repetition rate and frequency stable TEA lasers are discussed.