Frequency-dependent graded reflectivity mirror: characterization and laser implementation

We present a theoretical and experimental investigation of a new family of variable reflectivity mirrors, based on frustrated total internal reflection and interference effects. These mirrors are sensitive to frequency in the sense that their transverse reflectivity distribution changes significantly as a function of the frequency of light. The mirror reported here shows total power reflectivity changes of 50% within 8.0 GHz. The mirror was tested as the output coupler of an unstable resonator in a Nd:YAG laser working in the free-running regime. This configuration was compared with the standard stable multimode resonator configuration. The beam divergence was reduced by more than 1 order of magnitude and the output power was reduced by only 10%. The laser resonator mode competition that is due to the frequency-dependent mirror reflectivity distribution is discussed.