Investigation of the stability of laser discharges

Experimental and analytical investigations have revealed that negative ion processes affect both the steady discharge characteristics and the plasma stability of high power, carbon dioxide lasers. Computations including the pertinent negative ion attachment/detachment reactions have successfully modeled the measured steady properties of these volume-dominated discharges. However, the theoretical stability analysis indicates that conditions favoring ionization instability are readily achieved. Experimental detection of systematic plasma fluctuations confirms that ionization instability induced by molecule attachment reactions leads to the formation of running striations. As anticipated theoretically, these are removed by the addition to the original gas mixture of molecules such as CO and hydrogen which detach electrons from the atomic oxygen negative ion. Additional studies indicate that very small concentrations of plasma produced impurities such as NO, nitrous oxide, and nitrogen dioxide adversely affect discharge stability through their influence on negative ion processes.