Investigation of microdamage to dielectric coatings by laser radiation

An experimental investigation was made of the behavior of microdefects in refractory oxide and sulfide-fluoride dielectric coatings in the prethreshold range of exposure to laser radiation. The results obtained demonstrated clearly that the centers of optical breakdown in ZnS and SrF₂ (or MgF₂) coatings were strongly absorbing microinhomogeneities, whereas in coatings made of ZrO₂ and SiO₂ neither the concentration of microinhomogeneities (of > 1 μ size) nor their dimensions were affected by the action of a pulse (or a series of pulses) of power density just below the threshold.