Ultrafast mid-infrared high harmonic and supercontinuum generation with n₂ characterization in zinc selenide

Polycrystalline ZnSe is an exciting source of broadband supercontinuum and high-harmonic generation via random quasi phase matching, exhibiting broad transparency in the mid-infrared (0.5-20 μm). In this work, the effects of wavelength, pulse power, intensity, propagation length, and crystallinity on supercontinuum and high harmonic generation are investigated experimentally using ultrafast mid-infrared pulses. Observed harmonic conversion efficiency scales linearly in propagation length, reaching as high as 36%. For the first time to our knowledge, n₂ is measured for mid-infrared wavelengths in ZnSe: n₂(λ=3.9 μm)=(1.2±0.3)×10^-14 cm²/W. Measured n₂ is applied to simulations modeling high-harmonic generation in polycrystalline ZnSe as an effective medium.