Abstract

A common method of coupling unstable resonators is adjoint coupling through a hole. In this configuration, a portion of the magnified beam in one resonator is injected, as a demagnified beam, through a hole into the neighboring resonator. If the hole is small, diffraction effects are important. We show that the mutual coupling-strength of the two unstable resonators is roughly proportional to the hole size. The amplitude of the mutual coupling parameter oscillates as the position of the coupling hole is varied with respect to the optical axis. The absolute maximum value of mutual coupling takes place when the hole is on the optical axis. We show results for a strip unstable resonator and a three-dimensional resonator, and we discuss an interpretation of the mutual coupling strength in terms of Fresnel zones.

© 1990 Optical Society of America