Mirror electrode for laser initiated discharge channels

A reflecting waxicon has been demonstrated to generate long, smooth, CO2 laser induced breakdown plasmas in atmospheric pressure gases including nitrogen, argon, and air. A waxicon or compound axicon is a mirror consisting of two concentric cones which form a W-shaped cross section. The protruding central cone of the waxicon also functions as an electrode for laser guided electrical discharges. In contrast to conventional mirrors, this waxicon design produces nearly uniform laser intensity in a fixed length of breakdown plasma. The length of the laser induced breakdown plasma has been measured as a function of incident laser power and agrees well with predictions of a ray tracing code.