Efficient femtosecond traveling-wave optical parametric amplification in periodically poled KTiOPO4

We report, for the first time to our knowledge, high-power femtosecond trav eling-wave optical parametric amplification by use of periodically poled KT iOPO4. With a single pass through a 4-mm-long sample of 1.23-mm thickness w e achieved 40% internal conversion efficiency and 5 mu J of single-pulse id ler energy near 3.8 mu m, using only 75 mu J of energy from the output of a conventional 1-kHz Ti-sapphire regenerative amplifier. The 210-fs-long idl er pulses were almost transform limited. We discuss the specific problems e ncountered in high-power parametric conversion, mich as unwanted quasi-phas e-matched upconversion processes for polarization configurations that utili ze the largest (d(38)) nonlinear coefficient and the related formation of c olor centers (gray tracking) in KTiOPO4. (C) 1999 Optical Society of Americ a OCIS codes: 190.4970, 190.7110, 320.7110, 190.2620, 190.4400, 160.4330.