Characterization of All-optical, Microwave-free NV-Diamond Photoluminescence at Low Magnetic Fields

All-optical (AO), microwave-free magnetometry using nitrogen-vacancy (NV) centers in diamond is attractive due to its compatibility with a broad range of samples and reduced experimental complexity. In diamonds with NV ensembles at ppm-scale concentrations, magnetic-field-dependent photoluminescence (PL) features emerge at low magnetic fields (<2 mT) due to resonant dipolar interactions between NV centers. Here, we demonstrate AO-PL changes from hyperfine interaction with nitrogen nuclear spins, and correlate them with avoided energy level crossings created by interactions between NVs along both identical and different crystallographic orientations within the diamond host. We observe that the maximum AO-PL contrast favors optical illumination intensity orders of magnitude below the NV optical saturation intensity and indicates a dependence on NV concentration. Our findings suggest that low-field AO measurements with NV ensembles may achieve comparable magnetic sensitivity to conventional microwave-based techniques, paving the way for new research avenues in sensitive magnetometry with less system complexity; low size, weight, and power; and other advantages.