Excess noise in low Fresnel number unstable resonators

Numerical calculations of excess noise factors in low Fresnel number unstab le resonators are described in detail. Computed mode profiles in one transv erse dimension together with associated Petermann K-factors are presented; dynamical considerations such as injected wave excitation are also examined . The properties of the zero-order modes are consistent with virtual source theory and with a simple formula for K based on a geometrical optics appro ximation. While virtual source theory is asymptotic, we find that it can ma ke good predictions for Fresnel numbers as low as unity. Full numerical cal culations are however needed to determine accurate mode profiles and K-fact ors in some regimes, A new technique for calculating accurate higher-order mode profiles is also developed and this is employed to evaluate K-factor d ependencies of the first two higher-order even modes. (C) 1999 Elsevier Sci ence B.V. All rights reserved.