Optical degradation of high- power ionized argon gas lasers

The development, over the past several years, of high-power continuous duty argon ion lasers has encountered limitations in the form of a severe optical degradation problem. An absorbing film builds gradually on the optical components, which terminates the discharge tube. This layer absorbs a small fraction of the laser power, thermally distorts the optical components, and unbalances the optical cavity. In this way, the laser power that can be extracted is limited to some value far below the inherent capabilities of the active medium. Experimental investigations of Brewster's angle window degradation were performed on a large quartz bore laser capable of CW powers in excess of 100 watts. Methods of recognizing and measuring the extent of window damage were established. Contaminants generated by the discharge erosion of the electrodes and the bore structure proved to be the source of the problem. Studies of the transport processes suggested that the motion of charged particles under the influence of the plasma fields is the dominant mechanism by which the contaminants reach the terminal optics. On the basis of the understanding achieved during this study, various techniques to modify or prevent tile degradation were developed and assessed.