The Key Technology Of Magnetic Field Detection With Flux Concentrator Using Multi-Frequency Modulation On Solid Nuclear Spin In Diamonds

Nitrogen vacancy（NV）magnetic sensing technology uses the photoluminescence and spin resonance properties of diamond NV color center to control magnetic fields and microwaves to control the spin state of the NV color center,and then realize the measurement of the magnetic field.The technology has the advantages of high sensitivity,easy integration,high spatial resolution and biocompatibility,and has broad application prospects in biomedicine,material science,geophysics and other fields.The sensitivity and resolution of magnetic field measurements are mainly affected by the evolution and coherence of NV color center spin states.In this paper,by studying the spectrum of ¹⁴N core spin ultrafine structure,the method of improving magnetic sensitivity measurement is carried out,and the magnetic flux concentrator（MFC）combined with multi-frequency modulation method is used to simulate multi-frequency microwave and flux concentrator models and build a nuclear spin magnetic measurement platform Experimental verification is carried out,which improves the sensitivity of magnetic measurement and provides a feasible scheme for the realization of miniaturized NV magnetometer.The main research contents of this paper are as follows:（1）The combination of multi-frequency microwave and magnetic flux aggregation is proposed to realize high sensitive MR detection of ¹⁴N nuclear spin light detection.A multi-frequency microwave and magnetic flux aggregation model is established to optimize the modulation parameters of the multi-frequency excitation nuclear spin.The amplification of the slope of the nuclear spin modulation signal has been achieved by analyzing the ¹⁴N nuclear spin light detection MR spectral model.By designing and optimizing the magnetic flux concentrator model,the magnetic field magnification is obtained by simulation.The experimental platform of multi-frequency modulation nuclear spin magnetic measurement is built,which mainly includes optical path system,multi-frequency microwave field system,magnetic aggregation amplification magnetic field system and signal acquisition system,and the results of multi-frequency nuclear spin magnetic measurement are obtained.（2）This research focuses on the magnetic measurement method of multi-frequency continuous wave steady-state magnetic detection and combined flux aggregator.The continuous wave steady-state magnetic measurement method was used to compare the spectral line signal contrast,line-width and frequency resolution of nuclear spin and electron spin,among which the nuclear spin frequency resolution was 79 Hz and the electron spin frequency resolution was 1.37 MHz.Furthermore,by studying the comparison of the slope of modulated signal under single-frequency microwave and multi-frequency microwave excitation,it is proved that multi-frequency microwave can modulate the increase of signal slope and further improve the sensitivity of the system.Using the magnetic measurement method of the flux aggregator,sensitivity is 250 p T·Hz^-1/2.（3）In order to eliminate the influence of laser noise on fluorescence fluctuations,we characterize laser noise with different powers at different modulation frequencies and the electronic noise floor of the photodetector.We use a differential optical path approach,and differentially increase the magnetic sensitivity of the diamond NV color center by differentiating the detected fluorescence and laser co-input to the lock-in amplifier by using a double-balanced photodetector,and verify the effectiveness of the method by experimentally,which is 300 n V·Hz^-1/2before subtraction.,subtracted to 89.1 n V·Hz^-1/2,noise was reduced to one-third of the original level.