Abstract

The nitrogen-vacancy center in diamond exhibits a zero-phonon transition art 637 nm that has been assigned as an A→E transition at a site with trigonal symmetry.¹ Paramagnetic resonance studies revealed a triplet feature that was originally assigned to an excited state.² More recently, it was argued that the triplet signal actually arose from the ground state,^3,4We employ a new method of ultra-high-resolution nearly degenerate four-wave-mixing (NDFWM) spectroscopy, as well as persistent hole burning and electron paramagnetic resonance, to measure the metastable spin singlet excited-state lifetime and the g round-state spin-lattice relaxation time and also to prove that the ground state is indeed a triplet.

© 1991 Optical Society of America