Electronic structure of the nitrogen-vacancy color center in diamond

he nitrogen - vacancy (N-V) center is a point defect found in diamonds containing substitutional nitrogen impurities. It arises after exposure to ionizing radiation and subsequent thermal annealing. The physical structure of the center has previously been identified as a substitutional nitrogen atom located adjacent to a neutral carbon vacancy, but prior to this work knowledge of its electronic structure was very incomplete.;The results presented here are intended to establish the energy level structure of the N-V center unambiguously, using nonlinear laser spectroscopy in concert with paramagnetic resonance experiments. A new technique which achieves sub-Hertz resolution in nearly degenerate four-wave mixing (NDFWM) and optical two-beam coupling experiments was applied to determine the decay rates of excited states in the N-V center. Laser-enhanced EPR experiments were performed to assign spin character to the ground state. Fluorescent emission of the center was used to determine excited state energies. In particular, these results resolve earlier conflicting reports of the N-V ground state structure and offer a picture of state energies and dynamics consistent with all observations to date.;The principal results of this thesis may be summarized as follows. We show that the ground state of the center consists of a spin triplet ground state with a zero-field splitting of 2.88 GHz and a spin-lattice relaxation time of 1.170...