Fluorescence-Detected Magnetic Imaging Using NV Diamonds

      Nitrogen-vacancy (NV) centers in diamond, which combine high sensitivity to external magnetic fields and temperature with excellent spatial resolution, have attracted significant attention as quantum sensors. The electronic spin states of NV centers can be optically polarized through light excitation, and subsequently read out optically. Since the spin resonance frequency shifts with changes in external magnetic field and temperature, optically detected magnetic resonance (ODMR) measurements—combining microwave excitation with fluorescence detection—enable non-invasive, high-spatial-resolution sensing of magnetic fields and temperature.

      However, the sensitivity and reproducibility of ODMR signals are strongly influenced by multiple parameters, including optical excitation power, pulse timing, and microwave irradiation conditions.

      In this study, we investigated the effects of various parameters—such as laser modulation via an acousto-optic modulator (AOM), laser power, and the timing of laser and microwave pulses—on the ODMR signals of bulk NV diamond. We identified optimal conditions that maximize signal contrast and intensity while controlling spin polarization efficiency and thermal effects. These optimized conditions are highly effective as a preprocessing step for high-resolution magnetic field imaging, significantly improving the reproducibility and efficiency of ODMR detection. Finally, we applied the optimized parameters to magnetic field imaging of magnetic nano particles and solenoid coils.

      The results demonstrate the potential for high-precision, high-spatial-resolution magnetic field imaging in applications involving biological samples and magnetic materials.