Study On Pure Single Photon Source And Terahertz Wave Generation Based On Nonlinear Crystals

Nonlinear crystals have been developed along with the emergence of nonlinear optics,they have become an important material basis in many optical fields.They have great application value in laser modulation,holographic storage,quantum communication,etc.This paper mainly studies the important applications of nonlinear crystals in two aspects: single photon source and terahertz wave.On the one hand,single photon is an important information carrier for optical quantum information processing.High efficiency,high purity and deterministic single photon sources are important prerequisites for optical quantum computing and quantum secure communication.Spontaneous parametric down-conversion based on nonlinear crystal is one of the main methods for preparing single photon source.SPDC has the advantages of wide application range,low technical difficulty and simple operation steps,and has important research value.On the other hand,terahertz wave has broad application prospects in biomedical imaging,security inspection,material inspection and space communication.The preparation of terahertz source is the key link in the development of terahertz technology,although terahertz wave has developed rapidly over the past two decades,but the acquisition of high-energy,high-efficiency,tunable,low-cost,room-temperature terahertz source is still the focus of research.The main contents of the thesis include:(1)Preparing a pure single photon source based on a nonlinear crystals.Firstly,the single photon source generation process under group velocity matching conditions is theoretically studied and Hong-Ou-Mandel interference is introduced.Secondly,the process of KDP and its isomorphic crystals and PPKTP and its isomorphic crystals to produce a pure single photon source are numerically simulated.The thermal effects of PPKTP and its isomorphic crystals are discussed.The variation of the group speed matching wavelength of five crystal groups with temperature is analyzed.Taking PPCTA as an example,the joint spectrum distribution and HOM interference fringes are calculated as a function temperature.(2)Generating terahertz wave based on a nonlinear crystals.Firstly,the basic formulas of nonlinear difference frequency process are deduced,and the main factors affecting the efficiency of difference frequency conversion are analyzed.The concept and basic principle of cascaded difference frequency are proposed,and the coupled wave equations of cascaded difference frequency is derived.Secondly,the processes of generating terahertz wave based on PPKTP and its isomorphic crystals are simulated.The main parameters are summarized.The terahertz wave intensity of PPKTP and its isomorphic crystals in no cascade and cascade are simulated and compared.The influence of different conditions on the intensity of terahertz wave is analyzed and the quantum conversion efficiency of five crystals under cascaded difference frequency is calculated.