High Power Efficient 3.81 $\mu{\rm m}$ Emission From a Fiber Laser Pumped Aperiodically Poled Cascaded Lithium Niobate

We experimentally demonstrated a high power mid-infrared optical parametric oscillator that was pumped by a linearly polarized, pulsed Ytterbium-doped fiber laser. Cascaded parametric conversion was realized to obtain a higher conversion efficiency from the pump of 1.06 μm to the expected idler ~ 3.8 μm. A monolithic aperiodically poled magnesium-oxide doped lithium niobate was designed to compensate the phase mismatches of the nonlinear conversions from the pump to idler and the primary signal to idler simultaneously. The highest idler output power of 4.35 W at 3.81 μm was obtained under the pump power of 24.8 W at 1063.5 nm with pump-to-idler conversion efficiency of 17.5% and slope efficiency of 21.3%.