Transverse mode propagation and gain coefficients in a planar waveguide CO2 laser amplifier

The transverse mode propagation and amplification characteristics of a larg e electrode area, planar waveguide carbon dioxide laser amplifier have been investigated. Amplification of an imperfectly mode-matched input produces varying output beam quality with changing discharge conditions, through the modification of the propagation constants of the waveguide modes by the ga s thermal lens. For improved mode-matching to the amplifier, a near ideal T E1 output is obtained without discharge-induced variations. The maximum gai n coefficient for propagation in the fundamental mode is shown to be depend ent on the radio frequency discharge conditions through the frequency depen dence of the minimum stable power density. At 81 MHz, a gain coefficient of 0.65 m-l at 50-torr pressure is obtained.