Abstract

Coordinate-dependent mirrors in stableresonator lasers were used by us for: (1) obtaining transverse intensity distribution (TID) with predetermined non-Gaussian profile, without substantial decrease of power in comparison with the laser having ordinary homogeneous mirrors; (2) control of a mode structure of intraresonator field; and (3) obtaining the minimal diffraction-limited divergence output beam from a laser with large-volume active medium. Mirrors with a graded phase of reflection are sometimes needed, e.g., in the problem of transverse mode selection. But in most cases mirrors with graded amplitude of reflection are needed. For the latter case, reflection phase must be constant over the whole mirror surface that looks at active medium, otherwise diffraction losses became intolerable. Besides that, it is important to decrease the diffraction from narrow border areas between two parts of the mirror that have unequal reflectances. Methods for producing dielectric multilayer low-loss mirrors with various functions R(x, y) are described. Each mirror consists of 2 or 3 structures deposited successively. One structure has the thickness h(x, y) depending on coordinates. If two-grade mirror was needed, the inhomogeneous structure was deposited in the presence of thin plastic-film mask, electrostatically held on the substrate. Continuous variation h(x,y) was achieved by means of half-shadow deposition through a system of screens with calibrated holes. Formulas for the case of two screens with circular holes are suggested and confirmed experimentally.

© 1994 IEEE