Broadband conversion in an Yb:KYW-pumped ultrafast optical parametric oscillator with a long nonlinear crystal

We report the generation of 200-nm-bandwidth mid-infrared pulses at 3.5-µm from an optical parametric oscillator incorporating a 25-mm MgO:PPLN crystal and synchronously-pumped by chirped pulses from a fiber-amplified Yb:KYW laser. A long nonlinear crystal permits efficient transfer of the pump bandwidth into the idler pulses, achieves exceptional passive stability and enables pumping using chirped pulses directly from a fiber-amplifier, avoiding the need to use lossy pulse-compression optics.