Construction of long life argon lasers

The Tonks-Langmuir theory for the low-pressure positive column is reviewed and shown to be applicable to argon ion laser operation. Under these conditions ions formed in the plasma are accelerated and move by free fall to the wall. The sputtering effects of the ions on the plasma confining structure are evaluated for both a uniform insulator wall and a sectioned metal wall. A test is described where materials suitable for a sectioned column are compared. Of the materials tested (Ta, Mo, and graphite), graphite is shown to have outstanding properties for argon laser applications. A successful 1000-hour life test is described. Only slight sputtering damage was observed for the graphite plasma confining structure. Design considerations for long life argon lasers are discussed. These include choice of cathode, electrode shapes, plasma confinement structure, and tube processing. Solutions to the argon clean-up problem are described. Argon lasers built according to these recommendations are exemplified.