Efficiency optimization of the square pulse pumped terawatt level Optical Parametric Chirped Pulse Amplifier

Numerical simulations and analysis of a very efficient and stable non-collinear Optical Parametric Chirped Pulse Amplification (OPCPA) femtosecond system are presented. The system is optimized for a long (nanosecond), rectangular temporal profile and a flat-top spatial profile of the pump laser pulse. We show that a two stage system consisting of a multipass preamplifier and a time-sheared power amplifier operating around 850 nm and pumped by a 532 nm pulse can amplify pulses directly from a femtosecond oscillator up to multi-terawat levels with quantum efficiencies as high as 0.9. We also discuss practical schemes of the few-cycle multi-terawatt OPCPA systems employing different nonlinear crystals. The results of the Monte-Carlo simulations are used to balance the stability and efficiency of the parametric amplifier system.