Research On The Preparation Of Diamond Nv Color Centers By Femtosecond Laser

The nitrogen-vacancy color center(NV color center,NV)composed of a substituted nitrogen atom and a carbon vacancy is a typical representative of point defects in diamond.It is stable at room temperature with a high quantum yield,and can be optically manipulated.It shows great vitality in many frontier fields such as quantum sensing,quantum computing and high-resolution imaging combined with good chemical stability and biological compatibility of diamond.At present,the highprecision preparation and characterization of NVs often require complex operating environments such as low temperature or vacuum,customized masks,complex operating processes,huge optical systems,etc.The development of diamond precise micro-nano machining means is also limited by the high hardness and high stability of diamond.In addition,the preparation of NVs is also faced with the problems of limited depth,low yield,and lack of enough researches on related mechanisms to varying degrees.Femtosecond laser processing technology is being used in precise micro-nano machining of diamond due to its characteristics of true 3D and ability to process a wide range of materials at room temperature.To address the related problems of NV preparation mentioned above,the overall goal of this thesis is to develop an advanced diamond femtosecond laser processing method for the preparation of high-quality NVs in diamond.We set up an integrated processing-testing system for single color centers,and explored the rapid preparation of deep high-quality diamond NVs at room temperature in this thesis to further promote the applications of NVs and wide-bandgap materials including diamond in the field of cutting-edge technology.This thesis will provide an effective reference for the preparation of high-quality single-color centers in diamond and other wide-bandgap crystals.The main research contents are as follows:Firstly,the femtosecond laser preparation-characterization system of diamond precise micro-nano structures was established.In this thesis,a femtosecond laser spatial light modulation processing system was combined with a fluorescence confocal testing system to achieve an integrated processing-testing optical system of single-color centers.The system was highly integrated with stability,and the laser source and some of the optic elements could be flexibly replaced according to needs.The femtosecond laser micro-nano machining of the surface or interior of the diamond and other hard materials could be realized in the atmosphere with precision.In addition,the system was especially suitable for the preparation and characterization of diamond bulk single NVs.The successful establishment of the integrated optical system has laid a solid foundation for the subsequent experiments.Secondly,the related mechanisms and the process of the interaction between femtosecond laser and diamond were studied.A chemically assisted diamond ultraviolet femtosecond laser processing method was proposed to fabricate ultrafine composite micro-nano structures and spiral zone plates on diamond surface.After that,the internal laser modification of high-temperature and high-pressure diamond and CVD diamond was studied.The femtosecond laser processing capability on the surface and inside the diamond was verified overall.The non-diamond carbon attached to the diamond surface during laser machining was effectively removed by the chemically assisted machining method.The roughness of the pristine region and the laserprocessed region decreased from 20.5nm and 37.4nm to 0.64 nm and 9.4nm,respectively.The obtained optical devices showed good imaging/focusing effect and the device function was well realized,which verified the effectiveness of the proposed machining method.The study on the interaction between femtosecond laser and diamond surface/interior respectively provides an important experimental reference for the further improvement of laser machining accuracy in bulk diamond to induce single NVs subsequently.Thirdly,a method of preparing single NVs by spatial light modulation technologyassisted femtosecond laser direct writing was proposed,and the preparation of highyield single NVs by femtosecond laser at large depth in diamond was studied.When the femtosecond laser is incident into a diamond with a high refractive index,the ray bends at the interface and aberration arises,which leads to the longitudinal stretch of the laser focus.As a result,the energy density of the focus is reduced,which affects the processing accuracy severely.This thesis studied the aberration correction at large depth,discussed the principle of aberration correction and spatial light modulation algorithm;and the effectiveness of the aberration correction algorithm was verified by the actual laser processing results in diamond.Furthermore,the phase-modulated femtosecond laser was used to irradiate the bulk diamond then single NVs were prepared after high temperature annealing;and the properties of the single NVs were studied in detail.The relationship between the yield of single NVs and laser processing parameters was discussed,and the stability of the prepared emitters was verified.The actual depth of the obtained single NVs was 95?m with a statistical yield of 56±11%,which is the maximum depth reported in the related works of femtosecond laser-induced NVs in diamond.The prepared single emitters had good coherence and stability(> 5h),which proved the effectiveness of the spatial light modulation technology-assisted femtosecond laser machining method.Fourthly,the preparation and first-principles calculation of narrow optical linewidth single NVs were studied.The optical linewidth and the decoherence time of the single NV prepared in this thesis were 13.05±0.2MHz and 445±27.6?s respectively,which was an extremely narrow linewidth close to the lifetime-limited value of the excited state.Furthermore,in combination with the advantages of first-principles calculation,diamond supercells were established to simulate the surrounding environment of single NVs prepared by femtosecond laser direct writing method and commonly-used ion implantation method respectively,and the partial density of state,stress and dielectric constant corresponding to the models were calculated.The calculation results showed that the linewidths of NVs prepared by femtosecond laser direct writing were usually much narrower than those prepared by ion implantation,which may be due to the introduced defects in the ion implantation process,resulting in the change of stress in the surrounding environment of the NVs.The single NVs with extremely narrow linewidths prepared in this thesis can be used as light sources to generate indistinguishable photons,and can also be integrated with other micro/nano optical elements such as waveguides to be applied in quantum integrated optics.