Abstract

Dielectric multilayer graded reflectivity mirrors (GRMs) with a super-Gaussian (Gaussian raised to some power) radial variation of the reflectivity are known to reduce significantly the detrimental effects of hard edge diffraction in unstable laser resonators. Relatively low reflectivity GRMs consisting of a single graded thickness layer of high index have been produced in the past for use in high-gain lasers. Medium reflectivity GRMs consisting of one graded layer sandwiched in a quarterwave stack have also been demonstrated. In this work we propose GRMs with all layers graded simultaneously. Such geometries have several advantages: (i) they are suitable for high reflectivities, (ii) more degrees of freedom are available for the design (the multilayer structure and the mask shape can be varied), and (iii) the coating chamber does not need to be opened to introduce and subsequently remove a mask in the middle of the deposition process. In laser resonator use, not only the radial variation of the reflectivity but also the variation of the phase shift on reflection must be controlled to avoid an excessive deformation of the reflected wavefronts. This is especially important in high reflectivity GRMs because of the increased overall optical thicknesses.

© 1991 Optical Society of America