Observation of optical gain from NV⁻ center in diamond by femtosecond transient absorption

Single crystal diamonds with strong NV⁻ luminescence were prepared by high-pressure high-temperature method and followed by electron irradiation and annealing process. The stimulated emission and gain characteristics of NV⁻ diamond in femtosecond time scale are also studied using the transient absorption technique. Stimulated emission was observed at 660–800 nm, with an optical gain displayed in the range of 680–725 nm. Further test revealed that the optical gain lifetime is 3.5 ns and the gain coefficient is 0.16 cm⁻¹, demonstrating the potential realization of color center lasers.