High-Sensitive Magnetic Field Sensing and Imaging with Optical Microcavity Probe

Whispering gallery mode (WGM) microcavity magnetometers have emerged as a frontier in high-sensitivity magnetic field sensing, owing to their room-temperature operation capability, miniature footprint, and exceptional immunity to electromagnetic interference. In this work, we propose an innovative design of a fully encapsulated, probe-type WGM microcavity magnetometer with microsecond magnetic field response which overcomes application bottlenecks in complex environments. By precisely fabricating an epoxy-oxide microbottle cavity on the surface of a cylindrical magnetostrictive Terfenol-D substrate, we achieved a high-quality (Q) factor exceeding 106 with an outstanding detection sensitivity up to 25.2 nT/Hz1/2. The probe device can detect magnetic field frequencies from DC to 19 MHz, and in turn it can utilize magnetic fields to achieve a wide range (∼50 GHz) with fast scanning for the mode. We further report a magnetic field imaging technique, in which the probe serves as the sensing unit to accurately reconstruct the magnetic field distribution of the sample. This result highlights the broad application potential of our probe in magnetic field detection and imaging.