In the present work, ultrafast photon echo spectroscopy has been applied to investigate dephasing dynamics and excited state electronic structure of impurity N-V centers in diamond and Tm$\sp{3+}$-Tm$\sp{3+}$ centers. In the N-V center, quantum beat measurements revealed modulation frequencies of 0.63
± 0.02 GHz, 1.650
± 0.003 GHz, and 2.298
± 0.006 GHz which furnished excited state spin-spin splittings directly for the first time. Wavelength dependent studies of dephasing times showed conclusively the existence of a larger splitting of 46
± 2 cm$\sp{-1}$ in the excited E state. These results were found to be consistent with temperature dependent studies which reveal dephasing, near liquid-He temperatures, is dominated by a one-phonon direct dephasing process in the upper state with an activation energy of 68
± 16 cm$\sp{-1}$ has a two-phonon Orbach contribution to dephasing in the lower state with an activation energy of 39
± 5 cm$\sp{-1}.$ Experiments with circularly polarized light also revealed an interesting polarization selection rule originating from Zeeman coherence in the doublet E spin state of the $\sp3A$ ground state. A complete multi-electron model is presented which makes use of a previously undetected Jahn-Teller effect to explain all the observed excited state structure. An extension of these ultrafast techniques were applied to Tm$\sp{3+}$-Tm$\sp{3+}$ centers in YAlO$\sb3,$ permitting the first preliminary investigations of coherent dynamics on highly cooperative transitions. Dephasing times on the $\sp3F\sb4(\Gamma\sp2)$
→ $\sp1G\sb4(\Gamma\sp1)$ excited state transitions were found to increase from 35
± 2 ps to 61
± 6 ps with decreasing intensity of a resonant auxiliary cw laser which populates this transition in a controllable fashion. Temperature dependence studies revealed dephasing on this cooperative transition was dominated by a direct process with an activation energy of 157
± 16 cm$\sp{-1}$ at liquid-He temperatures. These results were consistent with expected dephasing rate dependence for interacting Tm$\sp{3+}$-Tm$\sp{3+}$ centers.
Quantum-beat spectroscopy has been used to observe excited states of the N-V center in diamond. For the 1.945-eV optical transition, direct evidence is presented for the existence of GHz-scale fine structure, together with a much larger 46-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ level splitting in the E state. An interference effect observed in transient four-wave-mixing response is explained with a polarization selection rule involving Zeeman coherence among magnetic sublevels. Also, detailed dephasing measurements versus temperature and wavelength have identified the decay mechanisms operative among the various states. A comparison of these results with ab initio calculations of excited electronic structure and interactions based on several multielectron models supports the conclusion that the N-V center is a neutral, two-electron center governed by a strong Jahn-Teller effect and weak spin-spin interactions. \textcopyright{} 1996 The American Physical Society.
The 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
± 0.003 ms. The first parity-allowed transition occurs to a triplet excited state at 1.944 eV with a lifetime of 13.3
± 0.2 ns. The first metastable singlet excited state is shown to have a lifetime of 265.3
± 0.6 ms at room temperature and its temperature dependence measured between 77 and 295 K. Through low temperature studies the mechanism for ground state spin-lattice relaxation is determined to be a two-phonon process involving 63 meV optical phonons. Finally, the origin of satellite lines in the persistent hole-burning spectrum is tentatively explained using our picture of the energy level structure and used to infer a zero-field spin splitting in the excited triplet state of 0.6 GHz.
Abstract Many applications of nitrogen-vacancy (NV) centers in diamond crucially rely on a spectrally narrow and stable optical zero-phonon line transition. Though many impressive proof-of-principle experiments have been demonstrated, much work remains in engineering NV centers with spectral properties that are sufficiently robust for practical implementation. To elucidate the mechanisms underlying their interactions with the environment, we apply multi-dimensional coherent spectroscopy to an NV center ensemble in bulk diamond at cryogenic temperatures. Our spectra reveal thermal dephasing due to quasi-localized vibrational modes as well as ultrafast spectral diffusion on the picosecond timescale. The intrinsic, ensemble-averaged homogeneous linewidth is found to be in the tens of GHz range by extrapolating to zero temperature. We also observe a temperature-dependent Stark splitting of the excited state manifold, relevant to NV sensing protocols.
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.