Preliminary analysis has indicated that laser radiation may alter microwave propagation in transparent solids by both electron avalanche and thermally induced plasmas. These effects may occur at fluence levels below that at which visible damage occurs. Temperature rises well below the melting point may create sufficiently dense plasmas to affect propagation. The dependence of propagation effects upon plasma density and size has been modeled. Effects of varying the initial temperature have been studied. Irreversible changes in microwave absorption are also considered. Effects are analyzed for a CdTe microwave modulator for CO2 laser radiation. Plasmas with densities 1015-1016 cm -3 are generated at temperatures 500-700 Ã‚Â°C in CdTe. At these densities, microwave propagation may be significantly affected. Microwave measurements of simulated plasmas have been carried out using metallic and resistive materials of different dimensions Comparison is made with theoretical models. An experimental setup using a high energy pulsed CO2 laser and a sensitive microwave reflectometer for measuring laser induced effects will be discussed.
R. S. Eng, R. S. Eng,
"Effects of laser damage processes on microwave propagation", Proc. SPIE 1438, Laser-Induced Damage in Optical Materials 1989, 14380B (1 November 1990); doi: 10.1117/12.2294420; https://doi.org/10.1117/12.2294420