  Wide field-of-view magnetic field microscopy has been realised by probing
shifts in optically detected magnetic resonance (ODMR) spectrum of Nitrogen
Vacancy (NV) defect centers in diamond. However, these widefield diamond NV
magnetometers require few to several minutes of acquisition to get a single
magnetic field image, rendering the technique temporally static in it's current
form. This limitation prevents application of diamond NV magnetometers to novel
imaging of dynamically varying microscale magnetic field processes. Here, we
show that the magnetic field imaging frame rate can be significantly enhanced
by performing lock-in detection of NV photo-luminescence (PL), simultaneously
over multiple pixels of a lock-in camera. A detailed protocol for
synchronization of frequency modulated PL of NV centers with fast camera frame
demodulation, at few kilohertz frequencies, has been experimentally
demonstrated. This experimental technique allows magnetic field imaging of
sub-second varying microscale currents in planar microcoils with imaging frame
rates in the range of 50 to 200 frames per second (fps). Our work demonstrates
that widefield per-pixel lock-in detection of frequency modulated NV ODMR
enables dynamic magnetic field microscopy.
