Mid-IR frequency comb source spanning 4.4-5.4 μm based on subharmonic GaAs optical parametric oscillator.

Broadband mid-IR output suitable for producing 1000-nm-wide frequency combs centered at 4.9 μm was achieved in a degenerate subharmonic optical parametric oscillator (OPO) based on 500-μm-long Brewster-angled orientation-patterned GaAs crystal. The OPO was synchronously pumped at 182 MHz repetition rate by 100 fs pulses from a Cr²⁺:ZnSe laser with the central wavelength of 2.45 μm and the average power of 100 mW.