Investigation of the Stability of Laser Discharges

Calculations indicate that thermal and/or vibrational instabilities will occur for most discharge conditions of importance in high power, cw carbon dioxide convection lasers. Computed characteristic growth times for these modes are typically on the order of 1 msec. The experimental investigations described herein have verified that it is the growth of disturbances in gas translational or vibrational temperature which is responsible for the discharge constriction observed in carbon dioxide laser plasmas. Moreover, because of the characteristic msec instability growth times, convection of the unstable portions of the medium out of the plasma region can effectively stabilize the discharge. The beneficial aspects of having homogeneous gas flow conditions and uniform electrical power deposition are suggested by the theory. Experimental results confirm that such plasma and fluid dynamic uniformity permits operation at increased electric power inputs and higher pressures. Extension of these results to CO lasers and electron-beam sustained plasmas is discussed. See also report dated Nov 74, AD-A004 418.