Features of high-frequency EPR/ESE/ODMR spectroscopy of NV-defects in diamond

The methods of high-frequency electron paramagnetic resonance (EPR), electron spin echo (ESE) and optically detected magnetic resonance (ODMR) are used to study the unique properties of nitrogen-vacancy (NV) defects in diamond in strong magnetic fields. It is shown that in strong magnetic fields ($\sim$3–5 T) there occurs an effective optically induced alignment of populations of spin levels resulting in filling the level $M_S$ = 0 and emptying of the levels $M_S$ = $\pm$1, that makes it possible to record ODMR using the change in the intensity of photoluminescence which reaches 10% at resonance. It is demonstrated that the efficiency of the alignment has the same order as in zero and low magnetic fields. The samples were preliminary studied by the ODMR method in zero magnetic fields that allowed accurate determination of the main parameters of the fine structure and hyperfine interactions with nitrogen nuclei, as well as dipole-dipole interactions between the NV center and deep nitrogen donors in the form of a nitrogen atom replacing carbon, N$^0$. Hyperfine interactions with the nearest carbon atoms (isotope $^{13}$C) were observed in the high-frequency ODMR spectra, that opens up opportunities for measuring the processes of dynamic polarization of carbon nuclei in strong magnetic fields using optical methods. It is assumed that narrow ODMR lines in strong magnetic fields can be used to measure these fields with submicron spatial resolution. A new method for recording ODMR of NV centers with microwave frequency modulation has been developed, which simplifies the technique of measuring high magnetic fields. A significant increase in the intensity of the ODMR signal was demonstrated when a strong magnetic field was oriented along the symmetry axis of the NV center.