Bandwidth extension and conversion efficiency improvements beyond phase matching limitations using cavity-enhanced OPCPA

The conversion efficiency and phase matching bandwidth of ultrafast optical parametric amplification (OPA) are constrained by the dispersion and nonlinear coefficient of the employedcrystal as well as pulse shaping effects. In our work we show that an enhancement cavity resonantwith the pump seeded at the full repetition rate of the pump laser can automatically reshapethe small-signal gain in optical parametric chirped-pulse amplification (OPCPA) to achieveclose-to-optimal operation. This new method termed cavity-enhanced OPCPA or C-OPCPAsignificantly increases both the gain bandwidth and the conversion efficiency, in addition toboosting gain for high-repetition-rate amplification. The goal in C-OPCPA is to arrive at acondition of impedance matching at all temporal coordinates, such that, in the absence of linearlosses, all the incident pump power is dissipated in the nonlinear loss element, i.e., convertedto signal and idler. The use of a low finesse enhancement cavity resonant with a low averagepower (