Laser‐induced microwave damage to dielectric materials

Dielectric samples of (1) pyroceram, (2) slip‐cast fused silica (SCFS), (3) impregnated slip‐cast fused silica (ISCFS), and (4) silicon nitride (Si3N4) were subjected to 10.6‐μm CO2‐laser radiation of irradiances up to 800 W/cm2. The increase in loss tangent at 6 GHz was measured both during and after laser irradiation using the microwave cavity perturbation technique. Surface temperatures of the samples were measured by an infrared thermometer. Theoretical and experimental evidence indicated that the complex permittivity changes were confined only to the surface layers (∼0.2 to ∼0.5 mm thick) of the samples.