Influence of the surface layer on the optical strength of lithium niobate

The technique of multiple frustrated total internal reflection is applied to demonstrate the existence of a surface layer in lithium niobate. The thickness and absorption coefficient of this layer are determined. It is shown that when the surface of lithium niobate is irradiated at subthreshold energy densities, a cumulative effect of the action of the laser radiation is observed. The dependences of the surface damage threshold on the pulse duration and the focal spot diameter are determined. Results of an experiment to study the dependence of the optical strength on the pulse duration confirm that lithium niobate has an absorbing surface layer.