Model for laser damage dependence on thin-film morphology

The high laser damage thresholds often reported for porous thin films are discussed in terms of point defects or small absorbing inclusions as sites of thin-film damage initiation. The model is based on the internal pressure built up upon laser heating at short times. The competing effects of short pressure relaxation distances and low thermal conductivity inherent in porous films are discussed. The model predicts that at thicknesses less than or equal to the neck or column diameter of a porous film, the effect of lower thermal conductivity should dominate and cause the films to exhibit lower laser damage thresholds than their denser counterparts.