Optical properties of the nitrogen-vacancy singlet levels in diamond

We report measurements of the optical properties of the 1042 nm transition of negatively charged nitrogen-vacancy (NV) centers in type-1b diamond. The results indicate that the upper level of this transition couples to the mₛ=±1 sublevels of the ³E excited state and is short lived with a lifetime of 1 ns. The lower level is shown to have a temperature-dependent lifetime of 462(10) ns at 4.4 K and 219(3) ns at 295 K. The light-polarization dependence of 1042 nm absorption confirms that the transition is between orbitals of A₁ and E character. The results shed light on the NV level structure and optical pumping mechanism.