Dual-chirped difference frequency generation (DFG) is an advantageous technique for generating the broadband mid-infrared (IR) idler wave, which is inaccessible by a population-inversion-based laser system. In principle, the generated idler wave may even suffer a spectrum broadening compared with the driving pulsed lasers if the pump and signal waves are oppositely chirped. However, broadband phase-matching is always the determining factor for the resulting efficiency and the bandwidth of the generated idler wave. In this study, specific to an oppositely dual-chirped DFG scheme, we derive the precondition to realize broadband frequency conversion, wherein a negative $(1/\unicode[STIX]{x1D710}_{p}-1/\unicode[STIX]{x1D710}_{i})/(1/\unicode[STIX]{x1D710}_{s}-1/\unicode[STIX]{x1D710}_{i})$ , in terms of the correlation coefficient of the group velocity ( $\unicode[STIX]{x1D70E}$ ), is necessary. However, most birefringence bulk crystals can only provide the required material dispersions in limited spectral regions. We show that the periodically poled lithium niobate crystal that satisfies an inactive Type-II (eo-o) quasi-phase-matching condition has a stable negative $\unicode[STIX]{x1D70E}$ and exerts the expected broadband gain characteristic across an ultra-broad idler spectral region $(1.7{-}4.0~\unicode[STIX]{x03BC}\text{m})$ . Finally, we propose and numerically verify a promising DFG configuration to construct a tunable mid-IR spectrum broader based on the broadband phase-matched oppositely dual-chirped DFG scheme.

中文翻译：

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通过产生相反的双啁啾差频产生有效的惰轮展宽

双啁啾差频生成 (DFG) 是一种用于生成宽带中红外 (IR) 闲散波的有利技术，这是基于种群反转的激光系统无法访问的。原则上，如果泵浦波和信号波是相反的啁啾，则与驱动脉冲激光器相比，产生的闲散波甚至可能遭受频谱展宽。然而，宽带相位匹配始终是最终效率和生成闲散波带宽的决定因素。在这项研究中，针对一个相反的双啁啾DFG方案，我们推导了实现宽带频率转换的前提条件，其中负 $(1/\unicode[STIX]{x1D710}_{p}-1/\unicode[STIX]{x1D710}_{i})/(1/\unicode[STIX]{x1D710}_{s}-1 /\unicode[STIX]{x1D710}_{i})$ , 根据群速度的相关系数 ( $\unicode[STIX]{x1D70E}$ ）， 有必要的。然而，大多数双折射体晶体只能在有限的光谱区域内提供所需的材料色散。我们表明，满足非活性 II 型（eo-o）准相位匹配条件的周期性极化铌酸锂晶体具有稳定的负 $\unicode[STIX]{x1D70E}$ 并在超宽闲散频谱区域内发挥预期的宽带增益特性 $(1.7{-}4.0~\unicode[STIX]{x03BC}\text{m})$ . 最后，我们提出并在数值上验证了一种有前途的 DFG 配置，以基于宽带相位匹配反向双啁啾 DFG 方案构建更宽的可调谐中红外光谱。