Outward-Inward Mode Coupled Unstable Resonator

A new type of unstable resonator is proposed, in which the inward mode is coupled with the outward mode through the reflection from a flat mirror located at the outlet of the confocal unstable resonator, and the output is taken from the aperture at the center of the concave mirror. The calculation based on the Fresnel-Kirchhoff integral showed the applicability of the new resonator to high-power and high-quality laser.