CHARACTERIZATION BY GUIDED-WAVE OF INSTABILITIES OF OPTICAL COATINGS SUBMITTED TO HIGH-POWER FLUX - THERMAL AND 3RD-ORDER NONLINEAR PROPERTIES OF DIELECTRIC THIN-FILMS

We study the reversible refractive index variations of optical thin films submitted to a high-power light flux. As a preliminary step, we study the thermorefractive coefficient partial derivative n/partial derivative T and the laser damage threshold of our materials. From the hypothesis of a localized optical Kerr-type effect, we use the m-line technique to estimate the nonlinear refractive-index coefficients n2 of TiO2, Ta2O5, and ZnS films with continuous illumination. Very large values of n2 are found for the films obtained by conventional evaporation condensation. On the other hand, the study of the change in the decoupling direction of a low-power light guided in a layer disturbed by a pulsed YAG laser gives a first analysis of the phenomena versus time.