Abstract

For some years now phase-unifying (PU) mirrors have been proposed as an alternative to graded reflectivity mirrors to improve the laser output beam quality.^1,2 These mirrors can also have the advantage of a simpler fabrication. The PU mirrors that exhibit a stepwise reflectivity profile along the radius are made by deposition of a proper coating on a substrate so that no phase variations are introduced in the reflected and transmitted beam. A properly shaped substrate (with stepwise groove) has been used in most cases to cancel out the phase difference between the two beams passing through the internal and external regions of the coupler.³ The same effect, however, can be achieved by the coating design without substrate machining.

© 1994 IEEE