MHz-rate burst-mode pump-probe laser for the FLASH FEL facility based on nonlinear compression of ps-level pulses from an Yb-amplifier chain

Abstract

The Free-Electron Laser (FEL) FLASH offers the world-wide still unique capability to study ultrafast processes with high-flux, high-rate XUV and soft X-ray pulses. The vast majority of experiments at FLASH are of pump-probe type and thus rely as well on optical ultrafast lasers. Here, a novel FEL facility laser is reported which combines the high average power output of Yb:YAG amplifiers with spectral broadening in a Herriott-type multi-pass cell and subsequent pulse compression to sub-100 fs durations. Compared to the previously employed laser utilizing optical parametric amplification, the new system comes with significantly improved noise figures, compactness, simplicity and power efficiency. It provides FLASH users 10 Hz repetition rate laser bursts with 800 s long trains of up to 800 pulses being optically synchronized to the FEL bursts with femtosecond precision. In the experimental chamber, pulses with up to 50 J energy, 60 fs FWHM duration and 1 MHz rate at 1.03 m wavelength are available and can be adjusted by computer-control. First cross-correlation measurements with the FEL pulses at the plane-grating monochromator photon beamline are demonstrated, proofing the suitability of the new laser for user experiments at FLASH