Flat-top picosecond pulses generated by chirped spectral modulation from a Nd:YLF regenerative amplifier for pumping few-cycle optical parametric amplifiers

In this paper we present an optically synchronized Nd:YLF regenerative amplifier optimized for use as a preamplifier in a few-cycle optical parametric chirped pulse amplification pump laser. In the pump amplification process we employ a combination of spectral modulation and chirping in order to control and optimize the temporal shape of the pulses. We report on a comparative study of two methods for generating near-flat-top or custom real-time variable-shaped pump pulses using either controlled chirp and shaping of the spectrum of the pulses seeding a regenerative amplifier or intracavity spectral filtering to broaden the gain bandwidth of the system. We show that in addition to minimizing gain narrowing and B-integral, the efficiency of the cascaded nonlinear processes of the parametric amplifiers can be increased.