LIGHT-INDUCED REFRACTIVE-INDEX MODIFICATIONS IN DIELECTRIC THIN-FILMS- EXPERIMENTAL-DETERMINATION OF RELAXATION-TIME AND AMPLITUDE

A two-beam setup based on the totally reflecting prism coupler is show n to be a powerful means of characterizing light-induced refractive-in dex modifications in dielectric thin films. Rise and relaxation times and amplitudes of thin-film refractive-index variations can be measure d. Some developments of the electromagnetic theory of prism coupling a re presented for Gaussian incident beams. Measurements made on a singl e Ta2O5 layer deposited on a silica glass are presented. Relaxation ti mes of a few milliseconds reveal the thermal origin of the phenomena. The thermal nonlinear coefficient of this Ta2O5 layer is nearly 10(-15 ) m(2)/W. (C) 1996 Optical Society of America