Cr:ZnS laser-pumped subharmonic GaAs optical parametric oscillator with the spectrum spanning 36–56 μm

Using a subharmonic optical parametric oscillator (OPO) based on orientation-patterned GaAs, we produced a broadband instantaneous output that spans 3.6-5.6 μm at 50-dB level (4.4-5.2 μm at 3 dB level), has 110 mW of average power, and is suitable for producing wideband-frequency combs in the mid-infrared. The OPO was synchronously pumped by a compact Kerr-lens mode-locked femtosecond Cr:ZnS oscillator with the central wavelength 2.38 μm and pulse repetition frequency 175 MHz.