RESUMO
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.
RESUMO
A carrier-envelope-phase-stable near-single-cycle mid-infrared laser based on optical parametric chirped pulse amplification and hollow-core fiber compression is demonstrated. A 4 µm laser pulse with 11.8 mJ energy is delivered from a KTA-based optical parametric chirped pulse amplification (OPCPA) with 100 Hz repetition rate, and compressed to 105 fs by a two-grating compressor with efficiency over 50%. Subsequently, the pulse spectrum is broadened by employing a krypton gas-filled hollow-core fiber. Then, the pulse duration is further compressed to 21.5 fs through a CaF2 bulk material with energy of 2.6 mJ and energy stability of 0.9% RMS, which is about 1.6 cycles for a 4 µm laser pulse. The carrier envelope phase of the near-single-cycle 4 µm laser pulse is passively stabilized with 370 mrad.