Visualized\nAxial Localization of Nitrogen-Vacancy\nCenter in Bulk Diamond Assisted by Radially Polarized Beam

Nitrogen-vacancy (NV) centers in bulk diamond, as an\nexcellent\nspin-based vector quantum sensor, require precise determination of\nthe axis orientation information. Here, we efficiently visualize and\ncompletely determine the NV axis orientation in bulk diamond, assisted\nby a radially polarized beam. We observe the rotational asymmetric\nfluorescence pattern of NV centers in bulk diamond, which is quite\ndifferent from that in nanodiamonds. Our theoretical calculations\nshow this difference is mainly due to the fact that the ratio between\nthe longitudinal and transverse electric field components of the focused\nradially polarized beam is greatly weakened in bulk diamond. This\nfluorescence pattern asymmetry can uniquely determine both the azimuth\nangle and the polar angle without degeneracy in bulk diamond. Then,\nwe verify these theories in bulk diamond with different orientations\nand nanodiamonds. The experimental result is consistent with that\nof the traditional method by measuring a series of optically detected\nmagnetic resonance (ODMR) spectra, and the error is less than 3.0\ndegrees. Our method can be easily extended to other solid-state spin\nsystems and shows great potential in quantum sensing of vector magnetic\nfields and nanoscale dynamic processes.