Improving the sensitivity of diamond NV center ensemble magnetometer based on microsphere

Diamond nitrogen-vacancy (NV) center ensemble magnetometer is a novel solid quantum magnetometer with high sensitivity and high spatial resolution, which can be used at normal temperature and pressure. However, the low fluorescence collection efficiency of the magnetometer in confocal optical system hinders further improvement in sensitivity. To solve the problem, based on silica microspheres, we propose a method to enhance the excitation and collection efficiency of NV center ensemble in massive diamond. Experimental results show, compared with the NV diamond magnetometer without microspheres, the photon collection efficiency of NV diamond magnetometer coated with a layer of microspheres is increased by 110%. Thus, the sensitivity of the NV center magnetometer is increased by 4 times to 5.3<i>&mu;T/&#8730;Hz</i>.