Research On Sensitivity Optimization Method Of Magnetic Detection For Ensemble NV Centers Of Diamond

Quantum magnetic sensing with an ensemble of nitrogen vacancy centers（NV）in diamond is developed based on the photoluminescence and spin magnetic resonance.Due to its high sensitivity,easy integration,high spatial resolution and superior biocompatibility,it has become a hot spot for research as a new generation of quantum magnetic sensing.In this thesis,several key factors of magnetic sensitivity optimization are studied and analyzed by studying the physical properties of NV center and its magnetic sensing mechanism.Aiming at the sensitivity optimization problem,the methods of pulse ODMR optimization and multi-frequency microwave full-axis excitation optimization was proposed.According to the experimental requirements,an optical experimental platform was built,and the feasibility of improving the sensitivity of magnetic detection in this thesis was proved through experiments.The main research contents of this thesis are as follows:（1）The structure,properties and magnetic sensing mechanism of NV center are described in detail.Several key factors for improving sensitivity are obtained by analyzing the magnetic field detection principle of optical detection magnetic resonance method,Ramsey time series method and spin echo method.（2）The confocal laser experiment system was built independently,mainly including optical system,uniform microwave field system,three-axis magnetic field system,signal acquisition and main control program of upper computer,etc.In addition,it has optimized optical path construction and control sequence.（3）The effects of microwave power and laser power on sensitivity are studied,optimizing both of them to achieve an optimal matching degree to increase system sensitivity,and the system sensitivity has further optimized by using pulse ODMR to suppress spectral line broadening.Finally,the sensitivity of the optimized pulse ODMR is improved by 2.88times,reaching 0.25 nT/Hz^1/2.（4）A dual-frequency microwave excitation method was used to solve the problems of low number of spins and high background noise of single-axis sensor.After superposition of dual-frequency microwave to realize synchronous regulation of all axial NV centers,experimental verification shows that the fluorescence contrast is about 3 times higher than that of uniaxial measurement,and the system sensitivity is about 14.3 times higher than that of uniaxial measurement,reaching 0.76 nT/Hz^1/2,which verifies the feasibility of improving the magnetic sensitivity of the system by full-axis excitation.