Efficient generation of green and UV light in a single PP-KTP waveguide pumped by a compact all-fiber system

We present simultaneous efficient second- (SHG) and third-harmonic generation (THG) in a single periodically-poled KTP waveguided crystal pumped by a compact femtosecond Yb-based laser in a condition of exactly phase-matched frequency doubling and nonphase-matched sum-frequency mixing processes. Internal conversion efficiency as high as 33% for SHG $(532nm)$ and $∼2%$ for the cascaded THG $(355nm)$ is reported. We believe this to be a clear experimental demonstration that strong third-harmonic can be generated in frequency doubling crystals through a nonphase-matched sum-frequency mixing process.