Efficient idler broadening via oppositely dual-chirped difference frequency generation

Abstract

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.

High power, widely tunable femtosecond MgO:PPLN optical parametric oscillator

“…[21] MgO-doped periodically poled lithium niobate (MgO:PPLN) can excel other nonlinear crystal, owing to wide transparency ranges, high effective nonlinear coefficient (27.4 pm/V) and quasi-phase matching (QPM). [22][23][24][25] In 2011, a two-color femtosecond MgO:PPLN OPO was demonstrated, synchronously pumped by a 7.4-W mode-locked Yb:KGW laser, providing 1.5 W of the signal with durations of 425 fs due to long pump pulse durations and no intracavity dispersion compensation. [26] In 2019, Hu et al proposed a novel bidirectional pumping technique to realize 1.04 W of the enhanced signal femtosecond MgO:PPLN OPO with a tunable signal spectrum across 1350 nm-1610 nm and idler spectrum ranges of 2938 nm-4529 nm, pumped by a fiber laser system.…”