A pulsed lock-in method for DC ensemble nitrogen-vacancy center magnetometry

This article proposes a scheme for DC nitrogen-vacancy (NV) center magnetometry that combines the advantages of the lock-in detection and pulse-type schemes. The proposed pulsed lock-in scheme does not lead to optical power broadening of optically-detected magnetic resonance, resulting in smaller linewidth, higher contrast, and better photon shot-noise-limited sensitivity compared with the conventional continuous-wave lock-in scheme. The optimal conditions, optimal sensitivity, and noise-suppression capability of the proposed method are compared with those of the conventional methods from both theoretical and experimental points of view. Through experimental measurements, an improvement by a factor of four in the sensitivity and an improvement by a factor of 60 in the minimum resolvable magnetic field (MRMF) compared with conventional method were obtained. Using a confocal experiment setup, the proposed scheme achieves an MRMF of 100 pT and a sensitivity of 3 nT·Hz^-1/2 corresponding to a volume-normalized sensitivity of 2.5 pT/(Hz·mm⁻³)^1/2, demonstrating the potential of this method in magnetic measurement applications with high sensitivity and high spatial resolution.