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We show the laser-driven acceleration of unprecedented, collimated (2 mrad) and quasi-monoenergetic (dE/E = 25%) electron beams with energy up to 50 MeV at 1 kHz repetition rate. The laser driver is a multi-cycle (15 fs) 1 kHz OPCPA system, operating at 26 mJ (1.7 TW). The scalability of the driver laser technology and the electron beams reported in this work pave the way towards developing high brilliance X-ray sources for medical imaging, innovative devices for brain cancer treatment and represent a step forward to the realization of a kHz GeV electron beamline., 9 pages, 3 figures, 1 table

Ultrafast electron dynamics drive phenomena such as photochemical reactions, catalysis, and light harvesting. To capture such dynamics in real-time, femtosecond to attosecond light sources are extensively used. However, an exact match between the excitation photon energy and a characteristic resonance is crucial. High-harmonic generation sources are exceptional in terms of pulse duration but limited in spectral tunability in the VUV range. Here, we present a monochromatic femtosecond source continuously tunable around 21 eV photon energy utilizing the second harmonic of an OPCPA laser system to drive high-harmonic generation. The unique tunability of the source is verified in an experiment probing the interatomic Coulombic decay in doped He nanodroplets across the He absorption bands. Moreover, we achieved intensities sufficient for driving non-linear processes using a tight focusing of the VUV beam. We demonstrated it on the observation of collective autoionization of multiply excited pure He nanodroplets., Comment: 12 pages, 5 figures, submitted to Nat. Commun

An upgraded version of the water-jet plasma X-ray source suitable for handling the 100 W power of the driving 1 kHz optical parametric chirped-pulse amplification (OPCPA) L1 Allegra laser system has been installed and commissioned at ELI Beamlines. Hard X-ray generation with the L1 Allegra laser is demonstrated for the first time., ELI Beamlines is a rapidly progressing pillar of the pan-European Extreme Light Infrastructure (ELI) project focusing on the development and deployment of science driven by high-power lasers for user operations. This work reports the results of a commissioning run of a water-jet plasma X-ray source driven by the L1 Allegra laser, outlining the current capabilities and future potential of the system. The L1 Allegra is one of the lasers developed in-house at ELI Beamlines, designed to be able to reach a pulse energy of 100 mJ at a 1 kHz repetition rate with excellent beam properties. The water-jet plasma X-ray source driven by this laser opens opportunities for new pump–probe experiments with sub-picosecond temporal resolution and inherent synchronization between pump and probe pulses.

A dual-output thin-disk picosecond laser operating at 100 W with 1 kHz repetition rate is reported in this Letter. By electronically adjusting the amplitude of the optical seed pulses that are injected into the laser cavity, the energy extracted from the gain medium can be shared between two pulses. Amplified double pulses are subsequently spatially separated into two independent beams by a fast Pockels cell, compressed in one common compressor, and frequency-doubled with ∼70% efficiency. This approach significantly decreases strain on the optics, as well as nonlinear effects, and is advantageous for power scaling.

Thin disk regenerative amplifiers have suitable characteristics to pump picosecond OPCPA. By optimizing the trigger pulse to the MZM, a dual-output laser operating at 100 W, 1 kHz repetition rate, compressed to the transform limit is reported.

We report on the progress in developing a high energy, 1 kHz OPCPA auxiliary laser (F-SYNC) which is intended to supplement the L1-Allegra beamline. The auxiliary pulses are synchronized to the main laser with femtosecond precision and arbitrary delay.

We report on the performance improvements of the L1 Allegra laser system. The pump laser upgrade with the thin-disk multipass amplifier allows for the energy ramp-up, while a newly developed synchronized auxiliary laser system provides the capability of the pump-probe experiments at arbitrary delays.

We report on a 1 kHz, 515 nm laser system, based on a commercially available 230 W average power Yb:YAG thin-disk regenerative amplifier, developed for pumping one of the last optical parametric chirped pulse amplification (OPCPA) stages of the Allegra laser system at ELI Beamlines. To avoid problems with self-focusing of picosecond pulses, the 1030 nm output pulses are compressed and frequency doubled with an LBO crystal in vacuum. Additionally, development of a thermal management system was needed to ensure stable phase matching conditions at high average power. The resulting 515 nm pulses have an energy of more than 120 mJ with SHG efficiency of 60% and an average RMS stability of 1.1% for more than 8 h.

The L1 Allegra is an OPCPA-based, high average power, high repetition rate laser system pumped by thin-disc based regenerative amplifiers currently under development at the ELI-Beamlines center in Czech Republic. The repetition rate is 1 kHz, pulse duration is below 15 fs and the wavelength centered around 820 nm with a maximum design pulse energy of 100 mJ. To avoid problems with self-focusing, a large portion of the system was placed inside vacuum, including the compressors and second-harmonic crystals for the last three 1030 nm pump lasers, the final three OPA stages, and the chirped mirror compressor. In order to reach the designed output energy of the whole system, the pump lasers need to be efficient, stable, and providing enough pump power for each of the amplification stages. Pulse compression of the final three pump lasers as well as efficient conversion to the second harmonic frequency in vacuum has posed several challenges and we report on their solutions and results. The vacuum environment causes difficulties for two main reasons. The first one is laser-induced-contamination (LIC) degrading the optical surfaces of dielectric gratings, mirrors and crystals, due to the presence of degassing components contaminating the vacuum chambers. The second reason is second-harmonic generation crystal mounts heating up, requiring regular phase matching corrections by rotation of the crystal mounts. The LIC problem was solved by regular cleaning of the chambers by means of an RF-plasma source, and the heating problem was solved by implementing active temperature stabilization by means of installing thermo-electric coolers on the crystal holders. To increase the efficiency of the second-harmonic generation, beam profiles of the pump lasers had to be improved. The original Faraday rotators, present in the linearly-designed regenerative amplifiers, caused non-Gaussian beam profiles due to the self focusing inside the rotators. By using KTF crystals inside a new type of rotators, the spatial profile of the pump lasers is more Gaussian, allowing the efficiency of the SHG to be higher, almost by 25%. All the solved problems recently allowed the system to reach a short pulse output energy of 56 mJ, paving a way to reach 100 mJ successfuly in the future.

Vacuum chambers are frequently used in high-energy, high-peak-power laser systems to prevent deleterious nonlinear effects, which can result from propagation in air. In the vacuum sections of the Allegra laser system at ELI-Beamlines, we observed degradation of several optical elements due to laser-induced contamination (LIC). This contamination is present on surfaces with laser intensity above 30 G W / c m 2 with wavelengths of 515, 800, and 1030 nm. It can lead to undesired absorption on diffraction gratings, mirrors, and crystals and ultimately to degradation of the laser beam profile. Because the Allegra laser is intended to be a high-uptime source for users, such progressive degradation is unacceptable for operation. Here, we evaluate three methods of removing LIC from optics in vacuum. One of them, the radio-frequency-generated plasma cleaning, appears to be a suitable solution from the perspective of operating a reliable, on-demand source for users.