The 4855-06 Resonant Phase Modulator is for 360 to 500 nm UV-Visible applications requiring resonant frequencies of 6.3 - 7.5 GHz. It is designed so the microwave phase velocity and optical group velocity through the crystal are matched. It is the perfect tool for atom trapping and cooling experiments involving cesium and rubidium because their resonant frequencies correspond to the ground-state energy splitting of these atoms. 8-32 and M4 mounting holes.