Sub-100 fs passively mode-locked holmium-doped fiber oscillator operating at 206 μ\mum

We demonstrate a simple and compact Holmium-doped fiber femtosecond oscillator, in-band pumped by a commercial Tm-doped fiber laser. The oscillator operates in the dispersion managed soliton regime at net zero intracavity dispersion and delivers >1  nJ pulse energy at 35 MHz repetition rate. The pulse duration directly at the oscillator output is 160 fs FWHM, close to the Fourier-limit of 145 fs FWHM. Using an additional nonlinear compressor stage, sub-100 fs FWHM pulse durations could be achieved. The nonlinear fiber compressor is implemented by a solid core highly nonlinear fiber for spectral broadening and a single mode fiber for pulse compression

The European XFEL Photocathode Laser

We present the Yb:fiber, Nd:YVO4 laser used to generate electrons from the RF photocathode gun at the European XFEL. The laser provides deep UV output pulses in 600 µs bursts with variable internal repetition rate (564 kHz to 4.5 MHz). Due to its robust architecture (mode-locked and synchronized fiber oscillator, Yb:fiber amplifiers and Nd:YVO4 gain blocks), the laser has operated with >99% uptime since January 2017. Using this laser, the XFEL reported energies of 17.5 GeV in July 2018, and simultaneous multi-mJ lasing in its three SASE beamlines. The laser offers two parallel outputs (1064 nm) with single pulse energies of >100 µJ and 11 ps width (FWHM). One output is converted to deep UV with efficiencies > 25%, and the second is used as a laser heater to reduce microbunching instabilities to increase SASE efficiency. Several state-of-art laser controls were implemented, including feed-forward algorithm to flatten electron charge along the bunch, active beam stabilization with ±10 µm jitter at the photocathode, state machines for hands-off end-user operation, and temporal pulse synchronization and drift compensation to the timing jigger of the electron bunches to less than 45 fs

Post-compression of multi-millijoule picosecond pulses to few-cycles approaching the terawatt regime

Advancing ultrafast high-repetition-rate lasers to shortest pulse durations comprising only a few optical cycles while pushing their energy into the multi-millijoule regime opens a route towards terawatt-class peak powers at unprecedented average power. We explore this route via efficient post-compression of high energy 1.2 ps pulses from a Ytterbium InnoSlab laser to 9.6 fs duration using gas-filled multi-pass cells (MPCs) at a repetition rate of 1 kHz. Employing dual-stage compression with a second MPC stage supporting a close-to-octave spanning bandwidth enabled by dispersion-matched dielectric mirrors, a record compression factor of 125 is reached at 70% overall efficiency, delivering 6.7 mJ pulses with a peak power of about 0.3TW. Moreover, we show that post-compression can improve the temporal contrast at picosecond delay by at least one order of magnitude. Our results demonstrate efficient conversion of multi-millijoule picosecond lasers to high-peak-power few-cycle sources, opening up new parameter regimes for laser plasma physics, high energy physics, biomedicine and attosecond science

Factor 40 pulse post-compression of 200 W in-burst average power pulses via single-stage multi-pass spectral broadening

We report nonlinear pulse compression of 1.2-ps, 2-mJ pulses. For spectral broadening, we use a Kr-filled Herriott-type cell with 22-roundtrips. After a chirped-mirror compressor, we measure 30-fs pulses, 80% transmission and an M$^2$ of 1.5×1.7

Postcompression of picosecond pulses into the few-cycle regime

In this work,we demonstrate postcompression of 1.2 ps laser pulses to 13 fs via gas-based multipass spectral broadening. Our results yield a single-stage compression factor of about 40 at 200 W in-burst average power and a total compression factor >90 at reduced power. The employed scheme represents a route toward compact few-cycle sources driven by industrial-grade Yb:YAG lasers at high average power

Post-compression of high average power picosecond pulses for few cycle generation and FEL pump-probe experiments

We demonstrate post-compression of 1.2 ps pulses to the few-cycleregime via multi-pass spectral broadening. We achieve compressionfactors of 40 via single and >90 via dual stage compression employingmJ pulses. Long term stability measurements show that suchpost-compression setup can be employed for FEL pump-probe experiments

Post-compression of picosecond pulses to four optical cycles

We report post-compression of 1.2 ps pulses into the few-cycle regime via multi-pass spectral broadening. We achieve compression factors of 40 in single and 93 in a dual stage scheme using a compact setup