5–17 μm few-cycle mid-infrared continuum through intra-pulse difference frequency generation in a BaGa₂GeSe₆ crystal driven at 2.4 μm

BaGa₂GeSe₆ (BGGSe) is a newly developed long-wavelength infrared (LWIR) nonlinear material that exhibits unique advantages in broadband infrared generation, attributed to its wide transmission range, large nonlinear coefficient, high laser damage threshold, and low dispersion property. Here, we systematically investigate the optimal intra-pulse difference-frequency generation process in BGGSe for an ultra-broadband LWIR output, by employing a tunable optical parametric amplifier as driving sources at the wavelengths of 2.0, 2.4, and 2.8 μm. The results demonstrate that the highest efficiency is achieved at 2.4 μm wavelength, simultaneously yielding the broadest spectral coverage of 5-17 μm, with a transform-limited pulse width less than two optical cycles. This study not only showcases a broadband, few-cycle LWIR laser from the BGGSe crystal but also offers practical insight for process optimization in broadband frequency down conversions, which could find usefulness in advanced molecular spectroscopic applications.