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 advantageous in terms of pulse duration but limited in spectral tunability in the vacuum ultraviolet range. Here, we present a monochromatic femtosecond source continuously tunable around 21 eV photon energy utilizing the second harmonic of an optical parametric chirped pulse amplification 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 collective processes in multiply excited helium nanodroplets, which have been previously observed only at free electron lasers.

In this work, we introduce two novel techniques for generating (quasi)monochromatic XUV radiation. One utilizes Bessel-Gauss beams and modulated gas media, while the other achieves continuous VUV tuning, enhancing versatility and efficiency for user applications.

We show the laser-driven acceleration of unprecedented, collimated (2 mrad divergence), and quasi-monoenergetic (25% energy spread) electron beams with energy up to 50 MeV at 1 kHz repetition rate. The laser driver is a multi-cycle (15 fs) 1 kHz optical parametric chirped pulse amplification 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 toward developing high-brilliance x-ray sources for medical imaging and innovative devices for brain cancer treatment and represent a step toward the realization of a kHz GeV electron beamline.

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.

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.

The extremely high electric fields sustainable by a plasma make the Laser Wakefield Acceleration (LWFA) the most compact technique to generate very highly relativistic electron beams in the GeV regime. The limited repetition rate and low efficiency of this technology has, to date, prevented to unleash its full potential as a unique source for basic research, biomedical applications and high flux sources of secondary radiations as hard X-rays and gamma-rays. In very recent years different works show a new research direction on electron acceleration at 1 kHz repetition rate. In this talk I will show the laser-driven acceleration of unprecedented, collimated (2 mrad) and quasi-monoenergetic (ΔE/E = 25%) electron beams with energy up to 50 MeV at 1 kHz repetition rate. The laser driver is the in-house developed L1-Allegra multi-cycle (15 fs) 1 kHz OPCPA system, operating at 26 mJ (1.7 TW). Said innovative results have been achieved in the new Laser Wakefield ALFA platform for user experiments developed at ELI-Beamlines. 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.

High-order harmonic generation (HHG) is a tabletop source of VUV radiation with many applications limited by a necessity for a specific photon energy and a monochromatized spectrum. The approach of using grating monochromators is not applicable for photon-hungry applications due to the high losses and pulse lengthening. We present experimental results of a wavelength-tunable monochromatic HHG source developed to tackle this challenge. We demonstrate this method using the L1 Allegra broadband OPCPA laser system at ELI-Beamlines and its conversion to UV used to pump the HHG.

We present experimental results of an intense wavelength-tunable and monochromatic HHG source, applicable for many user applications. We demonstrate this method using the broadband OPCPA and its conversion to UV pump.

In this study we explore the optimization of laser pulse duration to obtain the shortest possible pulse. We do this by employing a feedback loop between a pulse shaper and pulse duration measurements. We apply to this problem several iterative algorithms including gradient descent, Bayesian Optimization and genetic algorithms, using a simulation of the actual laser represented via a semi-physical model of the laser based on the process of linear and non-linear phase accumulation.

A new source of relativistic electrons based on laser wakefield acceleration has been recently built and commissioned at ELI-Beamlines user facility. This platform is proposed for the experimental study of radiation to electronics effects for components and devices dimensioned to laboratory and low Earth orbit applications, such as picosatellite class spacecrafts, e.g. CubeSat. The device is configured to represent energy range of relativistic electrons trapped in the Van Allen radiation belts, 0.1 – 10 MeV, and to study the effects of ultra-high dose rates radiation. The developed instrument includes a permanent magnet dipole electron beam spectrometer with luminescent screen for on-line beam parameters monitoring and vacuum to air interface. The electron beam acceleration experiment for up to 10 MeV energies have been performed using a nitrogen gas target. The generated electron beam has been used for the electronic device irradiation experiments. The profile of the beam, energy and dose imparted per laser pulse have been measured to evaluate efficiency of the device. The beam characterization technique has designed using the FLUKA Monte Carlo code. KE spectrometer is calibrated with conventional LINAC source of electrons.

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.

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.

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.

We discuss the current development of the L2-DUHA laser system at ELI-Beamlines. L2-DUHA is intended to be a high repetition rate, 100 TW-class laser system whose primary purpose is to serve as a driver for a laser-driven X-ray free electron laser. Optical parametric chirped pulse amplification (OPCPA) pumped by diode-pumped solid state lasers (DPSSL) was chosen as the method of broadband amplification for the laser. We discuss the key considerations in the design of the laser and focus primarily on the broadband front end, the high energy pump laser, and high energy OPCPA stages.

Stable picosecond supercontinuum generated in long crystals is an excellent means of seeding broadband, high-energy CPA systems. The generated output energy and spectrum can be almost three times as stable as the pump for a wide range of input pulse parameters. In this work, we show this is an intrinsic property for crystals longer than the filament and for a range of input energy values. We present a description of the stability mechanism in both the visible and infrared regions together with experimental data that support the theoretical explanation.

We report on the current state of readiness of the 1 kHz, 15 fs L1 ALLEGRA laser system for long term reliable operation driving user experiments based on HHG. The highly automated system, based on short pulse OPCPA, currently generates pulses with energy of 30 mJ at central wavelength of 820 nm.

We discuss the application of supercontinuum generation as a seed for stable few-cycle laser systems around 2.2 µm. The stability of the filamentation process is numerically examined in both the visible and IR domains.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Z. Hubka, R. Boge, F. Batysta, R. Antipenkov, J. Novak, M. Greco, E. Erdman, A. Spacek, L. Indra, K. Majer, J. T. Green, J. A. Naylon, P. Bakule, and B. Rus, "High energy, high average power, nonlinear frequency conversion and parametric amplification of picosecond pulses in vacuum," in Nonlinear Optics (NLO), OSA Technical Digest (Optica Publishing Group, 2019), paper NTh2B.7. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text R. Antipenkov, F. Batysta, R. Boge, E. Erdman, M. Greco, J. T. Green, Z. Hubka, L. Indra, K. Majer, T. Mazanec, P. Mazůrek, J. Naylon, J. Novák, V. Šobr, A. Špaček, M. Torun, B. Tykalewicz, P. Bakule, and B. Rus, "The Current Commissioning Results of the Allegra Kilohertz High-Energy Laser System at ELI-Beamlines," in Laser Congress 2019 (ASSL, LAC, LS&C), OSA Technical Digest (Optica Publishing Group, 2019), paper ATh1A.6. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

A passive peak intensity stabilization method based on optimal combination of Kerr nonlinearity and linear dispersion is presented. By analyzing the Kerr nonlinearity with a 3D numerical model it was found that if a Gaussian laser pulse acquires a certain amount of nonlinear phase and is consequently over-compressed to have sight negative chirp, the fluctuations in peak intensity caused by energy fluctuations are reduced. Thus, even if the energy of laser pulses fluctuates the peak intensity can be stabilized. The simulations for realistic pulse parameters show an increase in peak intensity stability by well-over an order of magnitude. We demonstrate this process experimentally using a thin disk pump laser at ELI-Beamlines