Double-Passed, High-Energy Quasi-Phase-Matched Optical Parametric Chirped-Pulse Amplifier

摘要

Quasi-phase-matched (QPM) optical parametric chirped-pulse amplification (OPCPA) in periodically poled materials such as periodically poled LiNbO(sub 3) (PPLN) and periodically poled KTiOPO(sub 4) (PPKTP) has been shown to exhibit advantages over the OPCPA in bulk nonlinear crystals. (GHH98, RPN02) The use of the maximum material nonlinear coefficient results in ultra-high gain with low pump peak power. Furthermore, propagation of signal, pump, and idler beams along one of the crystal principal axes eliminates the birefringent walk-off, reduces angular sensitivity, and improves beam quality. Relatively high level of parasitic parametric fluorescence (PF) in QPM OPCPA represents an impediment for simple, single-stage, high-gain amplification of optical pulses from nJ to mJ energies. PF in QPM is increased when compared to PF in critical phase matching in bulk crystals as a result of broader angular acceptance of the nonlinear conversion process. PF reduces prepulse contrast and conversion efficiency by competition with the signal pulse for pump pulse energy. Previous experiments with QPM OPCPA have thus resulted in pulse energies limited to tens of (mu)J. (JSE03) Optical parametric amplification of a narrowband signal pulse in PPKTP utilizing two pump beams has been demonstrated at a mJ-level, (FPK03) but the conversion efficiency has been limited by low energy extraction of pump pulse in the first pass of amplification. Additionally, narrow spectral bandwidth was the result of operation far from signal-idler degeneracy. Here we present a novel double-pass, broad-bandwidth QPM OPCPA. 1.2 mJ of amplified signal energy is produced in a single PPKTP crystal utilizing a single 24-mJ pump pulse from a commercial pump laser. (JFE05) To our knowledge, this is the highest energy demonstrated in QPM OPCPA.