Multipass active stretcher with large chirp for high-flux ultra-intense lasers

We demonstrate a novel active multipass stretcher that can deliver pulses with large chirp, adjustable chirped pulse duration, and great beam quality for a high-flux chirped-pulse amplification system. The stretcher is based on a Martinez-type stretcher and a regenerative amplifier structure, and the laser pulses can be amplified while they are stretched in the cavity. By controlling the round trip of the pulses running in the cavity, chirped pulses with more than 10 ns, even scaling to 30 ns, pulse duration and 20 nm bandwidth can be obtained very easily, which indicates a chirp rate of 0.5 ns/nm at 1053 nm central wavelength. Chirped pulses with several millijoules energy can be delivered with an Nd:glass-based intracavity amplifier used to compensate the losses. Benefited by the advantage of regenerative structure, the output pulses have excellent beam quality with M² of 1.1. Finally, the chirped pulses from this novel stretcher are compressed to 1.13 times the Fourier transform limit. With these advantages, this novel multipass active stretcher is significant for ultra-intense laser systems, especially for high-flux and high-energy 100 petawatt lasers.