Abstract
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.
Highlights
Optical parametric chirped-pulse amplification (OPCPA) has been a popular technique to amplify a broadband optical pulse in recent years[1, 2]
By introducing ‘L’ type configuration into two OPCPA stages, we theoretically analyzed its effect on the optimization of conversion efficiency, bandwidth and beam quality
In the high gain region such as OPCPA stage 1, the small signal gain does not recede due to the elimination of idler, but the gain is little higher than the traditional OPCPA of one crystal because the spatial walk-off is compensated between two crystals
Summary
Optical parametric chirped-pulse amplification (OPCPA) has been a popular technique to amplify a broadband optical pulse in recent years[1, 2]. In their OPCPA configuration, the nonlinear crystal must be quite long enough to provide enough signal gain which can lead to spatial gain narrowing and affect the signal output energy efficiency and stability Another recent work proposed cascaded extraction optical parametric amplification (OPA) for the design of high efficiency final amplifier and their numerical simulation showed a highest efficiency of 50%[18]. To output higher signal pulse energy, maximize the pump-tosignal conversion efficiency while ensuring gain broadband, our general idea is to incorporate the concept of eliminating idler from the specific design of pre-amplifier structure and OPCPA configurations. In this pre-amplifier structure, there are two traditional configuration OPCPA stages, and each amplification stage consists of two BBO crystals. The effect of pump-to-signal spatial walk-off, which is related to beam quality and energy stability, is discussed and compensated in our designed OPCPA configuration
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