Per pixel lock in detection based dynamic widefield magnetometry using quantum defects in diamond

Ultrasensitive microscale widefield magnetometry, based on magnetic resonance of nitrogen vacancy defects (NV) in diamond, have been applied to varied applications, for example imaging magnetic nanoparticles in living cells. However, in probing slow varying magnetic field these magnetometers are limited by trade-offs in per-pixel magnetic sensitivity and bandwidth of the sensor, limiting applications to imaging at millisecond timescales. For slow varying magnetic fields regime, lock-in detection of optically detected magnetic resonance spectrum (ODMR) has allowed pico-nanotesla magnetic field sensitivity maintaining DC to few Kilohertz bandwidth, however focusing all NV emitted light onto a single photodiode. In this work, we extend the lock-in measurements to a widefield area by using a lock in camera which can perform simultaneous per pixel demodulation up to few hundred kilohertz. We measure lock-in ODMR spectrum over hundreds of pixels, reconstruct static magnetic field and perform dynamic-widefield-magnetic field tracking. In addition we also obtain a single photodiode sensitivity of 54nT/sqrt(Hz) with magnetic field tracking at 500ms temporal resolution. We discuss further improvements in sensitivity that are required to enable millisecond scale magnetic imaging.