Partially Transparent Laser mirrors used for extracting output beams from laser resonators.

The function of an output Coupler is to transmit a part of the circulating intracavity Optical Power in order to generate a useful output of the laser. In the case of stable optical resonators, the output coupler mirror usually has a spatially constant output coupler transmission. Output couplers of unstable resonators can be very different, they may have a transversely variable reflectivity with a Gaussian or super-Gaussian profile, possibly even with total Reflection within some radius and total Transmission outside that radius.