LASER-HEATING OF A CAVITY VERSUS A PLANE SURFACE FOR METAL TARGETS UTILIZING PHOTOTHERMAL DEFLECTION MEASUREMENTS

The effects of a cylindrical cavity in a metal surface on the energy c oupling of a laser beam with the solid were investigated by using a ph otothermal deflection technique. The photothermal deflection of a prob e beam over the cavity was measured while the bottom of the cavity was heated with a Nd-YAG laser with a wavelength of 1064 nm. Cavities in three different materials and with two different aspect ratios were us ed for the experiment. Temperature distributions in the solid and the surrounding air were computed numerically and used to calculated photo thermal deflections for cavity heating and for plane surface heating. Reflection of the heating laser beam inside the cavity increased the p hotothermal deflection amplitude significantly with larger increases f or materials with larger thermal diffusivity. The computed phototherma l deflections agreed more closely with the experimental results when r eflection of the heating laser beam inside the cavity was included in the numerical model. The overall energy coupling between a heating las er and a solid is enhanced by a cavity.