A compact, self-compression-based sub-3 optical cycle source in the 3 – 4 μ m spectral range

We report on the experimental realization of a compact, Ti:sapphire laser-pumped mid-infrared light source, which delivers sub-3 optical cycle pulses in the 3 – 4 μ m spectral range. The light source employs difference frequency generation in potassium titanyl arsenate crystal by mixing the signal and idler waves from a commercial near-infrared optical parametric amplifier and subsequent optical parametric amplification in LiIO 3 crystal. The amplified sub-100 fs mid-infrared pulses are self-compressed down to sub-3 optical cycles by nonlinear propagation in few mm thick YAG, CaF 2 and BaF 2 crystals featuring anomalous group velocity dispersion in that spectral range. The self-compression is performed without the onset of self-focusing effects, hence maintaining a homogenous beam profile with energy throughput efficiency of above 90%, yielding the self-compressed pulses with sub- 30 μ J energy. Even larger self-compression factors (down to sub-2 optical cycles) were achieved in the filamentation regime, simultaneously producing an ultrabroadband supercontinuum, extending from the visible to the mid-infrared.