Multilayer dielectric coatings have been developed to provide high reflectivity and very low absorption for high power laser beams. Despite the progress made in the field of multilayer dielectric coatings, damage to these reflectors by high power laser b eams remains a problem in some applications. A microscopic view of surface damage induced by a KrF excimer laser beam at an energy density of about 3 Joules/cm2 is shown in the photograph. Colored effects are due to interference of reflected light from the various damaged coating layers. Damage induced by coherent light diffracted from small particles such as dust on the surface of the reflector can be seen in the form of concentric or linear ripples.