EXCESS NOISE FACTORS IN CIRCULAR UNSTABLE RESONATORS

We calculate excess noise factors (Petermann K-factors) for a circular confocal unstable resonator. Typical mode profiles, and the dependenc e of their eigenvalues and K-factors on cavity geometry, are presented . The calculations are based upon the 'virtual source' method as well as on a self-consistent solution of the Huygens-Fresnel integral equat ion. It is known that in a one-dimensional strip resonator, K-factors similar to 10(4) are possible; although simple arguments suggest that the K-factors in two dimensions should vary roughly as the square of t heir one-dimensional counterparts, this turns out to occur only in rec tangular symmetry and not in the circular case.