Visible color-center laser in diamond.

Laser action at 530 nm using H3 centers in diamond was observed with an efficiency of 13.5% at room temperature. Optical double-resonance experiments on N3 centers provided direct evidence for a (2)A metastable level. Its presence results in rapid decay of the excited (2)E state and low quantum efficiency as well as significant excited-state absorption in the N3 luminescence region.