Fabrication Of Single Centers In Diamond And High-resolved Measurement Of Emission Lifetime

Diamond has always been loved by its brilliance as a gem,but what actually attracts researchers is the excellent physical properties,stable chemical properties and various defects inside diamond.The point defects(ie,color center)in diamond formed by impurity atoms and lattice vacacies are widely applied in quantum information processing,quantum sensor,biomarker and high-resolution imaging etc.due to their stable single photon emission at room temperature and spin controllability,combined with advantages of diamond itself such as the high stability,robust acid and base resistance,and biocompatibility.Nowadays,the generation of color centers with excellent properties and high-resolution characterization of their properties generally require complex environments such as high temperature or low temperature,high or low pressure,resulting in a large and complicated equipment.Therefore,the research goal in this dissertation is to develop efficient fabrication methods and time-domain high-resolution measurement methods of single color centers in diamond at room temperature and ambient environment.And the feasible,efficient and fast production of the two most widely applied color centers in diamonds——the negatively charged nitrogen vacancy(NV~-)center and silicon vacancy(SiV~-)center,and high-resolution measurement of their fluorescence lifetime are explored in order to further promote their applications in many fields like quantum sensing,information technology and bio-medicine.The main content of this paper is divided into the following three parts:1.Enhanced generation of NV~-centers near the diamond surface by femtosecond laser technique was studied.The femtosecond laser was focused directly on diamond surface coated with a layer of silicon nanoballs.The Coulomb explosion of silicon nanoballs was triggered under the interaction of the strong femtosecond laser field,resulting in the injection of silicon ions into the diamond to enhance the generation of vacancies.The local heat ensuing from the Coulomb explosion around the irradiation area made the vacancies move to combine with nitrogen impurities,forming more NV~-centers.Compared with the area irradiated without nanoballs,the density of the created NV~-centers in the case with nanoballs was enhanced up to 15.5 times.In addition,the NV~-density could be controlled by adjusting the average power and the pulse number of the femtosecond laser.It was demonstrated in the experiment that the NV~-centers produced by the femtosecond laser illumination were all located near the diamond surface.2.Efficient and quick fabrication of single SiV~-centers with excellent optical properties by femtosecond laser technique was investigated.Based on the Coulomb explosion of silicon nanoballs triggered by femtosecond laser,SiV~-centers in diamond were produced by femtosecond laser technique.With subsequent annealing at 850°C,the vacancies moved and combined with silicon impurities to form single,multiple or clustered SiV~-centers.The generated single SiV~-centers presented stable and bright luminescence,good polarization property and short fluorescence lifetime.Similarly,all of the SiV~-center fabricated by the femtosecond laser illumination were close to the diamond surface.The results demonstrated that femtosecond laser could be utilized as a versatile tool to efficiently create SiV~-centers.3.The high-resolution lifetime measurement of fluorescence at few photons level emitted from SiV~-centers was achieved at room temperature based on single-photon frequency upconversion technique.The setup for frequency upconversion of fluorescence emitter from SiV~-centers was built,then a pump laser with 11 ps narrow pulse width was utilized as a high time-resolved probe to scan the decayed fluorescence from SiV~-centers in the time domain.By measuring the intensity of the upconversion light varying with the delay between the pump laser and the fluorescence,the decay curve of the SiV~-centers could be reconstructed,thereby obtaining the accurate fluorescence lifetime of the SiV~-centers.The effects of walk-off time between the pump laser and fluorescence in the nonlinear crystal and pulse duration of pump laser were analysed in the experiment,obtaining that the time resolution of the measurement system could reach 13 ps.