Ultraviolet four-wave mixing and phase conjugation with metastable color-center states in diamond

We report the observation of cw four-wave mixing and phase conjugation in the UV on the N3 color-center resonance in diamond. Using a jitter-free technique, the nearly degenerate four-wave mixing spectrum has been measured and the ultranarrow, 250-Hz-wide resonance analyzed to understand the metastable-state decay process responsible for the low quantum efficiency and large nonlinear susceptibility of this aggregated nitrogen structure. The results establish the existence and lifetime of a new excited state of the defect.