The Free‐Electron Laser (FEL) FLASH offers the worldwide still unique capability to study ultrafast processes with high‐flux, high‐repetition rate extreme ultraviolet, and soft X‐ray pulses. The vast majority of experiments at FLASH are of pump–probe type. Many of them rely on optical ultrafast lasers. Here, a novel FEL facility laser is reported which combines high average power output from Yb:YAG amplifiers with spectral broadening in a Herriott‐type multipass cell and subsequent pulse compression to sub‐100‐fs durations. Compared to other facility lasers employing optical parametric amplification, the new system comes with significantly improved noise figures, compactness, simplicity, and power efficiency. Like FLASH, the optical laser operates with 10‐Hz burst repetition rate. The bursts consist of 800‐μs long trains of up to 800 ultrashort pulses being synchronized to the FEL with femtosecond precision. In the experimental chamber, pulses with up to 50‐μJ energy, 60‐fs full‐width half‐maximum duration and 1‐MHz rate at 1.03‐μm wavelength are available and can be adjusted by computer‐control. Moreover, nonlinear polarization rotation is implemented to improve laser pulse contrast. First cross‐correlation measurements with the FEL at the plane‐grating monochromator photon beamline are demonstrated, exhibiting the suitability of the laser for user experiments at FLASH.

Dual-frequency comb spectroscopy permits broadband precision spectroscopy with high acquisition rate. The combs’ repetition rates as well as the mutual coherence between the combs are key to fast and broadband measurements. Here, we demonstrate a 1-GHz high-repetition-rate dual-comb system with high mutual coherence (sub-Hz heterodyne beatnotes) based on mature, digitally controlled, low-noise erbium-doped mode-locked lasers. Two spectroscopy experiments are performed with acquisition parameters not attainable in a 100-MHz system: detection of water vapor absorption around 1375 nm, illustrating the potential for fast and ambiguity-free broadband operation, as well as acquisition of narrow gas absorption features across a spectral span of 0.6 THz (600 comb lines) in only 5 μ s.

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We present recent developments of Yb-fiber laser front-ends tailored for a variety of special needs for high repetition rate accelerator driven FEL and UED facilities.

In dual-comb spectroscopy, the maximal spectral coverage and the minimal measurement time depend quadratically on the lasers’ pulse repetition rate. Here, we demonstrate a high-repetition rate 1 GHz dual-comb spectrometer based on low-noise Erbium-doped mode-locked lasers.