Numerical studies on hybrid resonators for a medium-size COIL

Abstract

A negative branch and a positive branch hybrid resonator, suitable for a laser with large optical cross section and small output coupling are explored numerically. The basis of the theory is the Fresnel-Kirchhoff integral equation, the calculations describe a passive resonator. The fabrication of cylindrical mirrors is difficult and deviations in mirror radius of curvature are possible. While a large concave radius of curvature of the mirror is allowed in the stable direction, a convex curvature is not tolerable. Near the ideal mirror parameters, the resonator in unstable direction is insensitive to mirror curvature variations, if the resonator length is appropriately adapted to the actual mirror curvatures. With respect to mirror tilt, the calculations show that in unstable direction the off-axis negative branch confocal unstable resonator is less sensitive than the off-axis positive branch confocal unstable resonator. In stable direction, the sensitivity to mirror misalignment is larger and dependent on the mirror curvature but independent of the unstable resonator part.