High-speed magnetic-field imaging via N-V ensemble and laser raster scanning

We present a technique based on an ensemble of nitrogen-vacancy (N-V) centers in diamond capable of imaging magnetic fields with high spatiotemporal resolution and sensitivity. A focused laser beam is raster scanned using an acousto-optic deflector and N-V center fluorescence is read out with a single photodetector, enabling near shot-noise-limited imaging. The method operates in what we term quasi-continuous-wave optically detected magnetic resonance (qCW-ODMR), a regime closely related to pulsed-ODMR schemes used to mitigate power broadening. In this qCW regime, N-V centers experience short optical pump pulses for spin polarization and readout while the microwave field continuously drives the spin transitions. We systematically characterize this regime and show that the spin response is governed by a tunable interplay between coherent evolution and relaxation, determined by the temporal spacing between pump laser pulses. Notably, the technique does not require precise microwave pulse control, thus simplifying experimental implementation. To demonstrate its capabilities, we image time-varying magnetic fields from a microwire with submillisecond temporal resolution. This approach enables flexible spatial sampling and, with our diamond, achieves nT/√Hz-level per-pixel sensitivity, making it a promising platform for imaging weak, dynamic magnetic fields in biological and other complex systems.