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Mid-infrared band 3-5μm laser light source has important applications in many fields such as medical treatment, basic science, communication, industry and so on. Subject to the limitation to available efficient gain media in the mid-infrared band, the traditional methods of laser generation and amplification, such as regenerative amplification, are no longer applicable. In order to produce broadband and high-energy mid-infrared laser, in this paper 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-frequency generation (DFG) process is used to implement the generation of mid-infrared laser via CPPLN. In the differential frequency process, the pump light used is 800 nm and the wavelength range of signal light is 0.95-1.6 μm . By calculating the dispersion curve of CPPLN crystal, the phase mismatch of difference frequency generation process with different signal lights is obtained. Under the condition of quasi-phase matching, CPPLN with deliberately poling structures is designed and used to provide phase mismatch compensation in a broad bandwidth. The designed structure can meet the generation of mid infrared laser in 1.6~5μm band according to the numerical simulations. The conversion efficiency of mid-infrared laser with different wavelengths at different positions in the crystal is obtained by using nonlinear coupled wave equations and fourth-order Runge-Kutta method. The results show that the mid-infrared laser covering 1.6~5μm can be produced efficiently in a single CPPLN crystal, with an average conversion efficiency of about 15%. The theoretical analysis and numerical simulation on the designed CPPLN crystal can provide good schematic reference and theoretical support for further experimental exploration on generation of mid-infrared laser.

Structure design and numerical simulation of chirped periodically polarized lithium niobate crystal for broadband mid-infrared laser generation