Eigenvalues of a nonconfocal laser resonator with an output-coupling aperture.

A nonconfocal laser resonator that has output-coupling apertures has been analyzed using the matrix eigenvalue technique. Numerical calculations of eigenvalues and eigenfunctions are performed for the interesting resonator consisting of one plane mirror with a coupling aperture and one spherical mirror. The effects of the coupling aperture are also discussed for several kinds of modes when both the mirror and coupling- aperture Fresnel numbers vary. It is found that the power loss of the TEM(00) mode becomes nearly constant in a finite range of the mirror Fresnel number. In such a range, the major source of a resonator loss is the power coupling through an aperture, and the coupling loss can be estimated independently of the loss caused by the spillover at mirror edges.