Mode properties of a strip confocal unstable resonator with saturable gain.

The asymptotic analysis technique for calculating the modes of unstable strip resonators is extended to include the effects of a saturable but otherwise uniform gain. Utilizing simultaneous forward and backward (in time) propagation and the Rigrod gain formula, an iterative algorithm is employed to find the intensities inside a resonator. In contrast with Fox-Li type iterations, this scheme converges rapidly and gives all the higher modes. Mode properties at critical Fresnel numbers are examined as a function of gain saturation, which is seen to reduce mode degeneracy.