Performance Analysis of Decentered Unstable Resonators.

Abstract : The purpose of this study was to examine the mode eigenvalues, far field beam quality, and far field beam steering of decentered, unstable resonators. The resonators examined had magnifications of 2.0 and equivalent Fresnel numbers in the range 9.3 or = N sub eq or = 9.9. The resonator modes were calculated by the asymptotic method of Horwitz. Two equivalent Fresnel numbers for the decentered resonators were defined. The fundamental and second-order mode eigenvalues exhibited periodicities in the equivalent Fresnel numbers. The mode separation was observed to be a function of the amount of decenter and the two equivalent Fresnel numbers. The cusps of the first two eigenvalues were cyclic in N sub eq. The far field integrated intensity was computed for spot sizes of one, two, and three Airy disks. The percentage of total power deposited in a given spot size increased as the decenter increased. Beam quality instabilities were observed in all modes. The beam steering angles of the first four modes were calculated. The angles fluctuated about the optic axis as the decenter was increased. The fundamental mode had significantly lower beam steering than the higher-order modes.