We present the design and experiment of a broadband optical parametric chirped-pulse amplifier (OPCPA) which provides high conversion efficiency and good beam quality at 808 nm wavelength. Using a three-dimensional spatial and temporal numerical model, several design considerations necessary to achieve high conversion efficiency, good beam quality and good output stability are discussed. To improve the conversion efficiency and broaden the amplified signal bandwidth simultaneously, the nonlinear crystal length and OPCPA parameters are analyzed and optimized with the concept of dissipating amplified idler between optical parametric amplification (OPA) of two crystals configuration. In the experiment, an amplifier consisting of two OPCPA stages of ‘L’ type configuration was demonstrated by using the optimized parameters. An amplified signal energy of 160 mJ was achieved with a total pump-to-signal efficiency of 35% (43% efficiency for the OPCPA stage 2). The output bandwidth of signal pulse reached 80 nm and the signal pulse was compressed to 24 fs. The energy stability reached 1.67% RMS at 3% pump energy variation. The optimized OPCPA amplifier operates at a repetition rate of 1 Hz and is used as a front-end injection for the main amplifier of SG-II 5PW laser facility.
To obtain high energy, high efficiency Nd: glass preamplifier used in certain host device, a Nd:glass regenerative amplifier system has been designed. By adjusting the single pass gain and carefully optimizing the cavity mode, the small-scale self-focusing effect in the gain medium was effectively controlled. Maximum pulse energy of 21mJ, pulse width of 2.6ns was obtained at the repetition frequency of 1Hz, corresponding to a high optical to optical conversion efficiency of 11% and amplification ratio of 108. The pulse to pulse energy stability was < 2% rms during 2 h continous operation. The laser has a good beam quality of M2=1.5. The spectrum was measured to be at center wavelength of 1052.915nm.
Design and experimental demonstration of a high conversion efficiency OPCPA pre-amplifier for petawatt laser facility
