In this study, we present the experimental proof of concept of the polarization-based filled-aperture coherent combination of two distinct broadband (sub-20 fs transform limited pulse duration at around 795 nm central wavelength) optical parametric chirped pulse amplification systems in free space. An average combination efficiency of 90 % is demonstrated.

The L2-DUHA Laser (Dual-beam Ultra-fast High energy OPCPA Amplifier) designed to provide 100 TW-level pulses at 50 Hz is being developed at ELI-beamlines. The front end will provide the seed for 100 TW pulse train and also synchronized multi-mJ, sub 50 fs, 2.2 μm auxiliary output at 2 kHz, both generated via supercontinuum. The near-IR branch centered around 820 nm is amplified in two OPCPA stages and stretched to 1.5 ns. The beam in the mid-IR branch is combined with a 1030 nm beam in DFG to generate a mid-IR beam centered around 2.2 μm, amplified in three OCPA stages and compressed.

The L1-Allegra laser (1 kHz, 50 mJ pulse energy, 15 fs pulse duration) developed at ELI-Beamlines [1] in Czechia is already being used for various scientific experiments. The femtosecond synchronization project (referred to as F-SYNC) aims to dramatically improve the experiments with L1-Allegra. Therefore, we have developed an independent auxiliary laser system inspired by the design of the L1-Allegra front-end [2], [3] with an output energy of approximately 13 mJ at 1 kHz and a bandwidth that supports compression to < 20 fs. In essence, F-SYNC consists of a master oscillator, a fiber seed distribution system, a pump laser with grating compressor [4], a supercontinuum (SC) seed [5], and 3 stages of optical parametric chirped pulse amplification (OPCPA).

The F-SYNC project introduces a high-energy OPCPA laser system capable of producing up to 13 mJ output compressible to <15 fs. It achieves fs-level synchronization and arbitrary timing delay with the L1 Allegra laser system (both 1 kHz), enhancing pump-probe experiments.

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.

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.

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.

Allegra laser system is one of the main laser sources of the ELI-Beamlines facility in the Czech Republic. The system is designed to operate at 1 kHz and >100 mJ output with the pulse duration of <15 fs at 820 nm central wavelength. The main role of the laser system includes driving plasma X-ray and high harmonic (HHG) secondary sources at ELI-Beamlines facility. In this submission we present the most recent results on the optimization of high-energy OPCPA amplification stages and discuss the operational performance of the laser system.

The Allegra femtosecond laser system is the main driver for high harmonic and plasma x-ray secondary sources at ELI-Beamlines operating at a 1 kHz rep rate. The system is based on OPCPA technology and consists of seven amplification stages pumped by thin-disk picosecond lasers. It is designed to reach 30 mJ output in the first phase of operation and to be ramped up to 50 mJ by engaging an additional pump laser. The amplified pulse is compressed to sub-20fs by an array of chirped mirrors and higher order dispersion is pre-compensated for by a Dazzler AOPDF in the front-end. In this paper we present the overview of Allegra system and the current status of deployment with a special focus on the high average power OPCPA in vacuum.

For most extreme light applications, a reliable and stable driver laser is crucial to successful experiments. As lasers grow in energy and peak power they become increasingly complex and more failure modes are introduced to the system as a whole. For this reason it is prudent to develop a laser with simplicity, repeatability, and durability in mind. With the wide commercial availability of high quality, inexpensive fiber components, much of the required pulse conditioning for seeding high energy laser systems can take place entirely in fiber. This allows for much of the laser front end to be compact, alignment-free, and computer controlled with potentially dramatic savings in cost and space on the optical table. Here we explore some of the current trends in fiber-based front ends for high peak power laser systems. The requirements for any given high peak power laser are always quite different and fiber front ends are enormously customizable, so here we present two basic versions of fiber front ends which are used at the ELI-Beamlines facility which resemble other common fiber front end architectures.

We report on the design and performance of a fiber-based, multi-channel laser amplifier seed pulse distribution system. The device is designed to condition and distribute low energy laser pulses from a mode-locked oscillator to multiple, highly synchronized, high energy amplifiers integrated into a laser beamline. Critical functions such as temporal pulse stretching well beyond 100 ps/nm, pulse picking, and fine control over the pulse delay up to 300 ps are all performed in fiber eliminating the need for bulky and expensive grating stretchers, Pockels cells, and delay lines. These functions are characterized and the system as a whole is demonstrated by seeding two high energy amplifiers in the laser beamline. The design of this system allows for complete computer control of all functions, including tuning of dispersion, and is entirely hands-free. The performance of this device and its subsystems will be relevant to those developing lasers where reliability, size, and cost are key concerns in addition to performance; this includes those developing large-scale laser systems similar to ours and also those developing table-top experiments and commercial systems.

We report on the status of the high repetition rate, high energy, L1 laser beamline at the ELI-Beamlines facility. The beamline is based on picosecond optical parametric chirped pulse amplification (OPCPA) of pulses from a mode-locked Ti:Sapphire oscillator and has a target energy/repetition rate of 100 mJ/1 kHz with < 15fs pulse duration. The OPCPA pump lasers use thin disk technology to achieve the high energy and average power required to pump such a high energy, high repetition rate broadband amplifier. Here we report on the progress in beamline development and discuss the technical challenges involved in producing such a system and their solutions. A major focus of the laser development is reliable, robust operation and long term stability; mechanical, optical, and control system architecture design considerations to achieve our goals of long term stability are discussed.

We report on a frequency-doubled picosecond Yb:YAG thin disk regenerative amplifier, developed as a pump laser for a kilohertz repetition rate OPCPA. At a repetition rate of 1 kHz, the compressed output of the regenerative amplifier has a pulse duration of 1.2 ps and pulse energy of 90 mJ with energy stability of σ < 0.8% and M2 < 1.2. The pulses are frequency doubled in an LBO crystal yielding 42 mJ at 515 nm.

We present a multistage 1 kHz OPCPA system, pumped by two frequency doubled thin disk regenerative amplifiers, delivering together 57 mJ at 515 nm. The OPCPA produces 8 mJ of amplified signal and is compressible to < 27 fs.

We report on a broadband OPCPA system, pumped at 515 nm by frequency doubled Yb:YAG thin disk lasers. The system delivers 11.3 mJ pulses at a central wavelength of 800 nm with a spatial beam quality of M2 = 1.25 and > 25% pump-to-signal conversion efficiency. The broadband pulses were demonstrated to be compressible to 12 fs using a chirped mirror compressor.

The ELI-Beamlines facility, currently under construction in Prague, Czech Republic, will house multiple high power laser systems with varying pulse energies, pulse durations, and repetition rates. Here we present the status of a high repetition rate beamline currently under construction with target parameters of 20 fs pulse duration, 100 mJ pulse energy, and 1 kHz repetition rate. Specifically we present the Yb:YAG thin disk lasers which are intended to pump picosecond OPCPA, synchronization between pump and signal pulses in the OPCPA, and the first stages of OPCPA.

We report on the progress of the front end development for a 100 J, 1030 nm amplifier at ELI-Beamlines and discuss requirements for and features of the front end. A particular emphasis is placed on the use of a fiber-based nanosecond pulse generator to produce arbitrarily shaped, stable pulses. Disadvantages of using such a fiber-based seed, such as a wandering baseline, are discussed and solutions are presented. A home-built RF harmonic synthesizer is shown to be capable of controlled sub-nanosecond shaping of optical pulses.