| The Nitrogen-Vacancy center is formed by combining carbon atomic vacancies with nitrogen atoms inside the diamond.Because of its stable physical properties at room temperature,stable luminescence,and easy manipulation of electron spins,diamond NV centers have become one of the hot research topics in the fields of precision vector micro-nano field measurement and quantum computing.Scientists have used chemical vapor deposition,electron beam radiation,ion beam injection,and femtosecond laser to prepare NV centers inside the diamond.However,there are still many difficulties and challenges in the efficient preparation and application expansion of high-quality,large depth,single NV centers:(a)The electron/ion irradiation processing equipment is bulky,and the solid particles introduced during the preparation process cause more interstitial defects around the NV centers,high residual stresses,and it is difficult to evaluate the processing effect immediately.(b)The special equipment for the femtosecond laser direct writing method is missing,and the processed depth is limited.Affected by the high refractive index scattering of diamond,the femtosecond laser direct writing of large depth and high-quality single NV centers is difficult,and the lack of in-situ "processing-detection" integrated NV center special laser direct writing equipment,which makes it difficult to utilize the advantages of good readout fidelity and long dephasing time of single NV centers.(C)high-precision magnetic field measurement still has room for improvement.The accurate measurement of magnetic field vector and gradient strength at the micro-Tesla level still faces challenges such as poor accuracy of NV center positioning and low efficiency of single NV center generation.To address the problems and challenges of the above diamond NV centers preparation equipment,preparation effect,and magnetic field detection application research technology,this thesis developed and validated a femtosecond laser-based diamond NV centers integrated processing test system,successfully prepared a large depth,high-quality,single NV centers inside the diamond,based on the large contrast optic detection magnetic resonance and good spin modulation performance,and finally the prepared the array of single NV centers with high sensitivity and consistency is successfully applied to high-precision static magnetic field vector and magnetic field gradient detection at a very small pitch.The specific research results are as follows.1.Development of an integrated femtosecond laser processing and testing system for diamond NV centers.The system integrates the femtosecond laser processing optical path,detection optical path,and electronic spin control system to realize a highly integrated and automated femtosecond laser integrated processing and inspection system for diamond NV centers.The marble fluorescence confocal system of the NV center processing and testing system is designed by Solidworks software modeling,and the system has a mounting accuracy of 0.1mm and a volume of only62cm*35cm*41cm.A dedicated subsystem for electronic spin control developed by FPGA replaces the general-purpose device and outputs a 6 ns high-precision timing control signal with a gated signal and dual-channel photon counting function.The Lab VIEW graphical programming platform is used to integrate the whole system with functionalized module control to achieve "one key" processing and testing tasks.The system integrates the processing,testing,and control systems in multiplexing,which lays the foundation for the low-cost,high-efficiency,and intelligent preparation of high-quality single NV centers and arrays.2.Preparation and detection of high-quality,large-depth,single NV centers inside the diamond.High-quality and single NV center arrays were prepared with high precision at a depth of 95 μm under the diamond surface using a spatial wavefront-shaping 515 nm femtosecond laser.The NV center array fluorescence confocal scanning image was clear,with the single NV centers yield was 56 ± 11 %,PLE linewidth was 13.05 ± 0.2 MHz,NV center processing error was about ± 0.2μm,the absolute distance was less than 0.4μm.A simplified gap defect model based on the first principle was used to elucidate the physical mechanism of large momentum particles such as photons relative to electrons/ions to introduce fewer gap defects around NV centers,which laid a theoretical foundation for the preparation of high-quality single NV centers by femtosecond laser.3.Diamond NV centers with large contrast optically detected magnetic resonance.Based on the integrated processing and testing system of the diamond NV center,the high readout fidelity of high-quality,large depth,single NV centers is fully utilized,and the contrast ratio of optically detected magnetic resonance spectrum detection at room temperature is achieved by 36%,which effectively reduces the noise-limited sensitivity and improves the magnetic field detection performance.The FWHM of the optically detected magnetic resonance spectrum is reduced to 0.379 MHz by the efficient coupling of the electron spin and the tertiary nuclear spin of the NV center under the action of the electron spin modulation subsystem,and the Rabi oscillation time of the prepared single NV centers exceeds 4 μs,the Rabi oscillation frequency reaches 4.33 MHz,the spin decay time 2*exceeds 2 μs,and the spin decay dry time2reaches 445 μs.It lays the foundation for the single NV centers to realize the detection of static weak magnetic fields and gradient fields with high accuracy.4.Highly consistent single NV centers static magnetic field vector and gradient measurements.Based on the integrated processing and testing system of the diamond NV center and the high-quality single NV centers,the NV axial magnetic field strength detection was performed,and the detection results were in high agreement with the static magnetic field strength simulation curve.The magnetic vector measurement Cartesian coordinate system was established for the axial measurement of the single NV centers,the equation for the axial magnetic field strength from the spin-Zeeman split to the coordinate axis of the NV centers was derived,and the magnetic field vector test results were consistent with the simulation results,and the measurement error was about ±0.00446 μT.A single axial micrometer gradient measurement of the static magnetic field was realized,and the measured magnetic field gradient at a very small pitch of 5 μm was-0.047 μ T/μm,which is a great improvement in both magnetic field sensing accuracy and magnetic field gradient detection accuracy.This thesis has done in-depth research on the integration of diamond NV center processing and testing system based on femtosecond laser direct writing.Through the design and implementation of the integrated processing and testing system of the diamond NV center,the separation of the NV center preparation and testing system is solved,and the preparation and testing efficiency are greatly improved.The problems of the large size of the electron/ion irradiation processing equipment,introduction of gap defects,and large residual stress of the prepared NV center were solved by the prepared array of large-depth high-quality single NV centers.Accurate measurement of large contrast optically detected magnetic resonance with static magnetic field vectors and static magnetic field gradients is achieved by using the high-quality single NV centers with high readout fidelity,narrow PLE line width,high processing positioning accuracy,and long spin dephasing time and decoherence time.The diamond NV center integrated processing and testing system developed in this thesis lays the equipment foundation for the low-cost,high-efficiency,and intelligent preparation of high-quality single NV centers and arrays,and paves the way for the wide application of NV center arrays in the fields of precision vector micro-nano field sensing,quantum bits,and biosensing. |
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