Efficient middle-infrared generation in LiGaS2 by simultaneous spectral broadening and difference-frequency generation.

We report a surprisingly broadband and efficient midinfrared pulse generation in LiGaS2 (Langasite, LGS) by invoking a simultaneous interplay of intrapulse difference-frequency generation, self-phase modulation, and dispersion. This cascaded mechanism expands the output bandwidth and output power at the same time. With 30-fs driving pulses centered at 1030-nm wavelength we obtain a broadband middle-infrared spectrum of 8-11 μm with an LGS crystal as thick as 4 mm, which is eight times longer than the walk-off length.