Pulsed laser-induced damage to thin-film optical coatings - Part II: Theory

In this paper the theories of avalanche ionization, multiphoton absorption, and impurity-initiated laser-induced damage are treated. At first inspection, none of these theories adequately describe the experimental observations of the variation of pulsed laser damage threshold in optical thin films with changes in material property, laser wavelength, pulse length, or film thickness. However, it is shown that the inclusion of a Mie absorption cross section for a range of dielectric impurity sizes provides a good description of the database with the impurity model. It is also shown that the thermal properties of the host film material and impurity are of considerable importance in explaining observed experimental data.