Efficient femtosecond traveling-wave optical parametric amplification in periodically poled KTiOPO(4)

We report, for the first time to our knowledge, high-power femtosecond traveling-wave optical parametric amplification by use of periodically poled KTiOPO(4) . With a single pass through a 4-mm-long sample of 1.23-mm thickness we achieved 40% internal conversion efficiency and 5microJ of single-pulse idler energy near 3.8microm , using only 75microJ of energy from the output of a conventional 1-kHz Ti:sapphire regenerative amplifier. The 210-fs-long idler pulses were almost transform limited. We discuss the specific problems encountered in high-power parametric conversion, such as unwanted quasi-phase-matched upconversion processes for polarization configurations that utilize the largest (d(33)) nonlinear coefficient and the related formation of color centers (gray tracking) in KTiOPO(4) .