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Summary
Mid-infrared band 3-5 laser light source has important applications in many fields such as medical treatment, basic science, communication, and industry. Owing to the limitation to available efficient gain mediain the mid-infrared band, the traditional methods of generating and amplifying lasers , such as regenerativeamplification, are no longer applicable. In order to produce broadband and high-energy mid-infrared laser, inthis work we combine quasi-phase matching technology and chirped periodically polarized lithium niobate(CPPLN) crystal for theoretical analysis and numerical design. The second-order nonlinear difference-frequencygeneration (DFG) process is used to implement the generation of mid-infrared laser via CPPLN. In thedifferential frequency process, the pump light used is 800 nm in wavelength and the wavelength range of signallight is 0.95-1.6 . By calculating the dispersion curve of CPPLN crystal, the phase mismatch of differencefrequency generation processes with different light signals is obtained. Under the condition of quasi-phasematching, the CPPLN with deliberately poling structures is designed and used to provide phase mismatchcompensation in a broad bandwidth. The designed structure can meet the generation of mid infrared laser in a1.6-5 band according to the numerical simulations. The conversion efficiencies of mid-infrared laser withdifferent wavelengths at different positions in the crystal are obtained by using nonlinear coupled waveequations and fourth-order Runge-Kutta method. The results show that the mid-infrared laser in a wavelengthrange of 1.6-5 can be produced efficiently in a single CPPLN crystal, with an average conversion efficiency of about 15%. The theoretical analysis and numerical simulation for the designed CPPLN crystal can provide good schematic reference and theoretical support for further experimental exploration on generation of mid-infrared laser
