We demonstrate a 3.2 µm mid-infrared source delivering 30 µJ, single-cycle pulses via two-stage bulk post-compression of a 10 W four-cycle OPCPA. By optimizing a tandem configuration of BaF2 and Si, we achieved a compressed pulse duration of 11 fs with a CEP stability of 145 mrad RMS. The output exhibited high spatio-spectral uniformity with small residual spatial and angular chirp. The reliability and long-term stability of the system are tested. Additionally, high-order harmonics were generated in ZnO with locked CEP. The demonstrated performance is ideal for strong-field and attosecond-science applications.

We report on the development of a carrier-envelope phase (CEP)-stable 1030 nm fiber-based laser system producing 6.2 fs pulses achieved via the multi-pass cell (MPC) post-compression technique with 402 W average power at 100 kHz repetition rate. This system employs an upgraded three-stage MPC compression scheme exhibiting excellent beam quality properties for this intensity region. Active stabilization locks the CEP noise below 430 mrad root mean square. This work represents the first demonstration of a coherently combined fiber laser system simultaneously achieving such exceptional average power, CEP stability and sub-two-cycle pulse durations. Similar to all other light sources of the Extreme Light Infrastructure Attosecond Light Pulse Source, this newly developed system is accessible to the international research community in peer-reviewed open user calls of the Extreme Light Infrastructure European Research Infrastructure Consortium.

A novel, to the best of our knowledge, millijoule-class femtosecond optical parametric amplification-based source is implemented as a seeder in the high-repetition-rate HF-PW laser of ELI ALPS. High energy seeding results in a bandwidth corresponding to a sub-19 fs transform limit, significant gain reduction in the Ti:Sa amplifier chain, and an extremely low amplified spontaneous emission relative intensity of 2 × 10 −14 with 10 J compressed energy. The combination of the achieved parameters with the routinely available 2.5 or 5 Hz repetition rate offers unprecedented opportunities for the generation of particles and high harmonics.

As we progress towards the limits of modern, high-peak power chirped pulse amplification in terms of gain bandwidth, various post-compression techniques are emerging to further shorten the duration of these pulses. Here, we present a spatio-temporally resolved simulation environment for the post-compression of energetic ultrashort laser pulses in thin dielectric media. Our approach applies an advanced Fourier transform technique, which helps to reduce computational costs drastically. We also provide experimental validation to support our simulations. In addition to showing excellent agreement with measured data from multi-TW, single-cycle post-compression experiments, the theoretical results revealed complex spatio-spectral and spatio-temporal features. The developed platform enables robust a priori optimization of post-compression setups across a broad energy range, from tens of millijoules to tens of Joules.

Frontends with extremely high intensity contrast are essential for PW-class laser systems. Such a Yb-pumped mJ-class OPCPA front-end was developed, exhibiting a pre-pulse temporal contrast of 10 -14 before -2 ps.

We demonstrate enhanced spectral broadening of femtosecond pulses (330 fs, 1030 nm, 5-200 kHz) in a hollow-core fiber (HCF) using CO2/helium gas mixtures. While increasing pure CO2 pressure broadens the spectrum and induces a Raman redshift, it causes substantial optical loss. Introducing a helium buffer enables strong broadening at reduced CO2 pressures, significantly decreasing loss. Propagating pulses through a 1-m-long, 300-μm-core HCF, we show that helium enhances spectral width, extends the Raman shift, and improves transmitted power by facilitating spatial cooling. This binary molecular/noble gas approach provides a robust, low-loss route for spectral engineering in HCFs.

We present a 10 mJ-class laser system based on a hybrid, femtosecond optical parametric and negatively chirped Ti:Sa-based amplification architecture. Output pulses with 13 mJ energy, 14.4 fs transform limited duration, and high spatio-spectral quality are reached at 100 Hz repetition rate centered at 788 nm wavelength. By compressing 1 mJ energy, a pulse duration of 15.5 fs is measured in combination with an intensity contrast higher than 1012 already 15 ps before the main pulse. The presented architecture can be a robust and reliable solution for seeding sub-17 fs high intensity lasers with ultrahigh contrast at up to 100 Hz repetition rate.

The post-compression of high peak power laser pulses can efficiently increase the peak intensity on target without the need to build additional amplification stages and enlarge the compressor optics. However, to our best knowledge, the spectral broadening of such pulses with different nonlinear media has not yet been investigated systematically. Here we performed an experimental campaign with mJ-class 25 fs pulses, where the conditions of high energy post-compression were emulated. Fused silica, sapphire, and YAG plates were tested for spectral broadening and compressibility while measuring the spatio-spectral properties of the broadened pulses. We conducted a series of numerical simulations to have deeper insight on the broadening process, to better understand the experimental results and to find optimum parameters for future experiments.

High intensity laser facilities require reliable frontend systems which can provide appropriate spatio-spectral properties, ultrahigh temporal contrast, high energy and ultimate long-term stability. These properties are, naturally, very challenging to acquire simultaneously and represent close to industrial requirements. Recent advances in ultra-intense laser systems have shown significant focus on the development of next generation frontend arrangements [1]–[4].

The ALPS Facility of ELI ERIC provides few-cycle light pulse sources to the international user community. A key group of beamlines utilizes the 1 mJ, sub-6 fs, 100 kHz fiber-based laser system, HR1, which supports attosecond high harmonic generation applications and time-resolved spectroscopy experiments. While the high repetition rate facilitates statistical analysis, it also puts a high thermal demand on beam delivery and targetry due to the high average power. In this paper, we present a laser system as a solution for the high demand of discrete repetition rates from 10 Hz to 10 kHz, spanning several orders of magnitude below the 100 kHz of the HR1 system. This apparatus, referred to as the HR Alignment system, is integrated into the same HHG beamline in the ELI ALPS facility where the 100 kHz HR1 system can also be operated. It offers tunable repetition rate (10 Hz to 10 kHz), carrier-envelope phase (CEP) stabilization, and delivers sub-6 fs pulses with 1 mJ energy. The system comprises an Yb:KGW frontend, two nonlinear compression stages based on multipass cell technology, and precisely designed chirped mirrors. Detailed characterization reveals excellent energy stability, beam quality, temporal contrast, and CEP stability below 300 mrad, all designed to match the pulse parameters of the HR1 laser. This compact, robust, and turnkey system provides high flux for reaction microscopy experiments based on high harmonic generation (HHG) and serves as a valuable asset for ultrafast research for external users of ELI ALPS.

The ELI-ALPS High Repetition Rate laser laboratory provides high-power, ultrashort laser pulses for statistical investigation of ultrafast phenomena [1]. Our laser systems deliver few-millijoule pulses in the near-infrared (1030 nm) at repetition rates up to 100 kHz. This high repetition rate enables experiments that require large number of observations, such as those resolving quantum-mechanical phenomena with single-photon sensitivity or studying events with rare occurrence.

We present a 10 mJ-class laser system for seeding petawatt-class Ti:Sa lasers based on a hybrid, femtosecond optical parametric and negatively chirped Ti:Sa-based amplification architecture. Output pulses with 13 mJ energy, 14.4 fs transform limited duration, and high spatio-spectral quality are reached at 100 Hz repetition rate centered at 788 nm wavelength. By compressing 1 mJ energy with bulk glass and positively chirped mirrors, a pulse duration of 15.5 fs is measured. The intensity contrast is higher than 10^12 already 15 ps before the main pulse. The presented architecture can be a robust and reliable solution for seeding sub-17 fs high intensity lasers with ultrahigh contrast at up to 100 Hz repetition rate.

The ELI ERIC facility offers international users ultrashort laser sources via the ALPS facility focusing on few-cycle laser drivers for attosecond pulses, particle beams and ultrahigh intensity interactions. The HR1 system supports attosecond high harmonic generation (HHG) and time-resolved spectroscopy at 100 kHz. However, its high repetition rate, while aiding statistical analysis, poses thermal challenges and limits certain applications requiring lower repetition rates. To address this, the HR Alignment laser system was developed for the HHG beamline at the ELI-ALPS facility. This new system delivers sub-6 fs, 1 mJ pulses with a tunable repetition rate (from 10 Hz to 10 kHz) and carrier-envelope phase (CEP) stabilization. It utilizes an ytterbium-doped potassium gadolinium tungstate front-end, multi-pass cell compression, and chirped mirrors. Characterization confirms excellent energy and CEP stability (below 300 mrad), beam quality and temporal contrast, matching the HR1 laser's performance. This compact, stable system provides high-flux attosecond generation for reaction microscopy enhancing ultrafast research in the ELI-ALPS facility.

We present the post-compression of 25 fs pulses with a flat-top beam profile in different nonlinear media. Fused silica, sapphire, and YAG plates were tested for spectral broadening and compressibility while measuring the spatio-spectral properties of the broadened pulses. To our best knowledge, such systematic investigation has not yet been carried out. The near-and far-field profiles show that no significant wavefront distortion occurred during the nonlinear propagation but the spatio-spectral homogeneity has a strong correlation with the material characteristics and the accumulated B integral. A series of numerical simulations were also conducted to have deeper insight on the broadening process and the impact of the material properties. The theoretical model also reveals the limitations of compressibility in the single thin plate arrangement and it can support the optimization of future, high-energy experiments.

Development trends of high intensity laser systems points in the direction of increasing the repetition rate towards 10 Hz and beyond, while reliability and stability is also greatly improved [1], [2]. Next generation of particle and high harmonic beamlines require stable temporal compression of the driver pulses together with high spatio-temporal quality. Operation of the HFPW laser of the ALPS Facility of ELI ERIC has been recently demonstrated at the 700 TW level at 10 Hz repetition rate [3]. Intensity contrast and spectral stability requirements of experiments push the boundaries of currently available laser frontends. Furthermore, the high repetition rate and consequently the high average power also put a high demand on the final amplifiers, and on the vacuum compressor optical elements.

We report on the development of a carrier-envelope phase (CEP) stable 1030 nm fiber-based laser system producing 6.2 fs pulses achieved via the multi-pass cell (MPC) post-compression technique with 402 W average power at 100 kHz repetition rate. This system employs an upgraded three-stage MPC compression scheme exhibiting excellent beam quality properties for this intensity region. Active stabilization locks the CEP noise below 430 mrad RMS. This work represents the first demonstration of a coherently combined fiber laser system simultaneously achieving such exceptional average power, CEP stability, and sub-two-cycle pulse durations. Similarly to all other light sources of the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI ALPS), this newly developed system is accessible to the international research community in peer-reviewed open user calls of Extreme Light Infrastructure European Research Infrastructure Consortium (ELI ERIC).

We investigate high rep-rate operation and spatio-spectral challenges in the petawatt laser of ELI ALPS. User readiness, next steps and potential issues of development towards the final 2 PW 17 fs output are also discussed.

Apodization was combined with thin plate post-compression of 30 fs laser pulses to achieve spatio-spectrally homogeneous broadened output. This method allows for simulating petawatt-class post-compression in small-scale experiments, while energy upscaling is in progress.