应用于宽带中红外激光产生的啁啾周期极化铌酸锂晶体结构设计及数值模拟

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

中红外波段3—5μm激光光源在医疗、基础科学、通信、工业等众多领域都有着重要的应用需求,而受制于中红外波段的增益介质,传统的激光产生及放大的方法如再生放大、多程放大、行波放大等已经不适用.为了产生宽带且高能量的中红外激光,本文结合准相位匹配技术和啁啾周期极化铌酸锂(CPPLN)晶体进行了理论分析.通过计算分析铌酸锂晶体的色散关系曲线,对CPPLN晶体的结构参数进行设计和调节.结合非线性耦合波方程组与四阶龙格库塔法对该晶体在800 nm激光的抽运下,与0.95—1.6μm范围内的信号光进行准相位匹配差频转换进行了数值模拟.研究表明,在单块CPPLN晶体中,结合准相位匹配技术,能够高效产生覆盖1.6—5μm的中红外激光.对CPPLN晶体产生中红外激光的理论分析和数值模拟,能够为进一步的实验探究等提供方案参考和理论支持.

Mid-infrared band 3–5μm 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 media in the mid-infrared band,the traditional methods of generating and amplifying lasers,such as regenerative amplification,are no longer applicable.In order to produce broadband and high-energy mid-infrared laser,in this work we combine quasi-phase matching technology and chirped periodically polarized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-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 in wavelength and the wavelength range of signal light is 0.95–1.6μm.By calculating the dispersion curve of CPPLN crystal,the phase mismatch of difference frequency generation processes with different light signals is obtained.Under the condition of quasi-phase matching,the 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 a1.6–5μm band according to the numerical simulations.The conversion efficiencies of mid-infrared laser with different wavelengths at different positions in the crystal are obtained by using nonlinear coupled wave equations and fourth-order Runge-Kutta method.The results show that the mid-infrared laser in a wavelength range of 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 for the designed CPPLN crystal can provide good schematic reference and theoretical support for further experimental exploration on generation of midinfrared laser.