Dual-chirped difference frequency generation (DFG) is an advantageous technique for generating the broadband mid-infrared 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 (PM) is always the determining factor on 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/υp-1/υi)/(1/υs-1/υi), in terms of the correlation coefficient of the group-velocity (σ), 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 (PPLN) crystal that satisfies an inactive Type-II (eo-o) quasi-phase matching (QPM) condition has a stable negative σ and exerts the expected broadband gain characteristic across an ultra-broad idler spectral region (1.7 μm - 4.0 μm). Finally, we propose and numerically verify a promising DFG configuration to construct a tunable mid-infrared (IR) spectrum broader based on the broadband phase-matched oppositely dual-chirped DFG scheme.
Zhong Haizhe, Hu Bin, Hu Saisai, Dai Shengying, Li Ying, Fan Dianyuan. Efficient idler broadening via oppositely dual-chirped difference frequency generation[J]. High Power Laser Science and Engineering, , (): .
