Quantum Diamond Microscope for Narrowband Magnetic Imaging with High Spatial and Spectral Resolution

The quantum diamond microscope (QDM) is a recently developed technology for near-field imaging of magnetic fields with micron-scale spatial resolution, under ambient conditions.  In the present work, we integrate a QDM with a narrowband measurement protocol and a lock-in camera, and we demonstrate imaging of radio-frequency (rf) magnetic field patterns produced by microcoils, with a spectral resolution of approximately 1 Hz. This rf QDM provides multifrequency imaging with a central detection frequency that is easily tunable over the megahertz scale, allowing spatial discrimination of both crowded spectral peaks and spectrally well-separated signals. The present instrument has a spatial resolution of approximately 2 μ⁢m, a field of view of approximately 300 × 300 μ⁢m², and a per-pixel sensitivity to narrowband fields of about 1 nT Hz^−1/2. Spatial noise can be reduced to the picotesla scale by signal averaging and/or spatial binning. The rf QDM enables simultaneous imaging of the amplitude, frequency, and phase of narrowband magnetic field patterns at the micron scale, with potential applications in real-space NMR imaging, ac susceptibility mapping, impedance tomography, analysis of electronic circuits, and spatial eddy-current-based inspection.