Optical coatings with variable reflectance for laser mirrors

Design procedures and fabrication techniques of variable reflectance dielectric mirrors for laser output couplers are proposed. The design criteria, based on the use of only one shaped layer in a multilayer structure, yield any peak value and shape of the reflectance profile. The deposition technique of the variable thickness layer consists of a sputtering process with a suitable mask interposed between the target and substrate. Results of a simple model that correlates the mirror parameters to mask diameter and position are presented. A few devices for a Nd:YAG laser have been proposed, characterized, and successfully tested in a laser resonator.