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提出了一种基于等周期PPLN晶体渐变式温度控制的宽带中红外差频产生(DFG)激光光源的设计新方案。理论研究结果显示,在固定抽运光波长条件下,闲频光/信号光的准相位匹配(QPM)波长接收带宽(BW)随着晶体两端温度梯度的增加而增加,但差频转换效率却随之下降。当抽运光波长固定为1.08μm时,在均匀温度条件下中红外闲频光的QPM BW约为8nm。固定晶体初始端的温度为30℃,当晶体两端的温度梯度分别设定为20℃、40℃和60℃时,闲频光的QPM BW可分别拓宽至35nm、80nm和136nm。与此同时,QPM带内相对差频转换效率分别下降至0.2、0.095和0.06。当晶体初始端的温度设定为90℃,仍保持晶体两端的温度梯度为60℃时,该宽带的闲频光QPM带向短波长方向平移,其波长覆盖范围为3.288~3.464μm。
A new design scheme of wideband mid-frequency infrared difference frequency generation (DFG) laser source based on equal-period PPLN crystal gradual temperature control is proposed. The theoretical results show that the bandwidth (BW) of quasi-phase matching (QPM) wavelength of idler / signal light increases with the temperature gradient at both ends of the crystal under the condition of constant pumping light wavelength, but the difference frequency conversion efficiency But then declined. When the pump light wavelength is fixed at 1.08 μm, the QPM BW of the mid-IR idler light at a uniform temperature is about 8 nm. The temperature of the initial end of the fixed crystal is 30 ° C. The QPM BW of idler light can be broadened to 35 nm, 80 nm and 136 nm, respectively, when the temperature gradient across the crystal is set to 20 ° C., 40 ° C. and 60 ° C., respectively. In the meantime, the QAM in-band relative difference frequency conversion efficiency drops to 0.2, 0.095 and 0.06, respectively. When the initial temperature of the crystal is set at 90 ° C and the temperature gradient at both ends of the crystal remains at 60 ° C, the broad band idler light QPM shifts to the short wavelength with a wavelength range of 3.288 to 3.464 μm.