NONDESTRUCTIVE EVALUATION OF THIN-FILM COATINGS USING A LASER-INDUCEDSURFACE THERMAL LENSING EFFECT

Laser-induced surface deformation is a widely used technique for study ing thin film coatings. In this technique the deformation is typically detected using the well known optical beam deflection technique. In t his paper we report a different technique for studying surface deforma tion by using an optical diffraction effect. In this detection scheme, the laser-induced thermal bump behaves as a curved reflection mirror which can either focus or defocus a second probe laser beam through op tical diffraction, depending on the specific geometry used. This surfa ce thermal lensing effect is demonstrated to be a sensitive and easy-t o-handle method for thin film characterization. The potentials of this technique and its advantages over the conventional method for thin fi lm absorption measurement and defect characterization are discussed.