Abstract

An interesting application of optical coatings in the laser field requires cavity mirrors with a particular reflectance profile (i.e., a Gaussian profile) along the coating radius. However, these devices generally introduce a phase distortion in the wave front of the laser beam. Real improvement in laser performance depends on controlling both the reflection intensity and phase profile. Traditional design procedures and thin-film deposition techniques are aimed at producing coatings with defined reflectance values at different wavelengths but uniform reflectance on the coating surface. In this work, the reflection and transmission intensity and phase at a single wavelength are examined, and a suitable design method for obtaining desired radial profiles is proposed. The phase front is generally required to be flat along the radius while, at the same time, the reflection intensity either decreases continuously from the coating center to the outside or has a jump at a particular radius value. Such performances are obtained with thin-film multilayer coatings in which one of the layers has a profiled thickness. This radially variable thickness is achieved by the aid of a properly shaped mask in a sputtering deposition apparatus. Coatings for Nd:YAG and CO₂ lasers are examined.

© 1990 Optical Society of America