Extreme Light Infrastructure Research Articles

GPE - a Compact Gamma-Ray Polarimeter with Energy Reconstruction Capability

We present here the design, expected parameters and performance tests of a compact detector, based on INTPIX4 sensing device, developed in the framework of the Extreme Light Infrastructure – Nuclear Physics (ELI-NP) project, capable of measuring both polarization and energy of gamma rays, in the high energy range above 1 GeV. The detector, based on electron-positron pair creation in the BetheHeitler process, has been tested with cosmogenic muons and will allow unique experiments at the ELI-NP facility.

Classification of laser beam profiles using machine learning at the ELI-NP high power laser system

The high power laser system at Extreme Light Infrastructure—Nuclear Physics has demonstrated 10 PW power shot capability. It can also deliver beams with powers of 1 PW and 100 TW in several different experimental areas that carry out dedicated sets of experiments. An array of diagnostics is deployed to characterize the laser beam spatial profiles and to monitor their evolution during the amplification stages. Some of the essential near-field and far-field profiles acquired with CCD cameras are monitored constantly on a large screen television for visual observation and for decision making concerning the control and tuning of the laser beams. Here, we present results on the beam profile classification obtained from datasets with over 14 600 near-field and far-field images acquired during two days of laser operation at 1 PW and 100 TW. We utilize supervised and unsupervised machine learning models based on trained neural networks and an autoencoder. These results constitute an early demonstration of machine learning being used as a tool in the laser system data classification.

Investigation of laser plasma instabilities driven by 527 nm laser pulses relevant for direct drive inertial confinement fusion

We report on a study of laser plasma instabilities with 527 nm laser pulses in an intensity range of 0.5×1013−1.1×1015 Wcm−2 and plasma parameters entering a regime that is relevant for direct drive inertial confinement fusion. Using the kilojoule high repetition rate L4n laser at the Extreme Light Infrastructure—Beamlines, more than 1300 shots were collected, and the onset and the growth of stimulated Brioullin scattering (SBS) and stimulated Raman scattering (SRS) were studied with a high confidence level. The measured onset intensities are 0.2×1014 Wcm−2 for SBS and 1.4×1014 Wcm−2 for SRS. At the maximum intensity, the total fraction of backscattered energy reaches 2.5% for SBS and 0.1% for SRS. These results are of high relevance for advanced concepts for inertial fusion energy, which rely on the use of 527 nm laser light to drive the implosion of the fuel target, and in particular, they can be used as a benchmark for advanced simulations.

The annealing setup and associated monitoring system of the ELIADE HPGe clover detectors at ELI-NP

We report a dedicated setup built in-house for the annealing of the HPGe clover detectors of the ELI-NP Array of DEtectors (ELIADE) γ-ray spectrometer, as well as the post-annealing testing of these detectors with the standard 60Co & 152Eu radioactive calibration sources employing conventional analog electronics. Both the design and assembly of the annealing setup were performed at the Extreme Light Infrastructure — Nuclear Physics (ELI-NP) facility, Măgurele, Romania. A `radiation damage annealing assembly kit' (NRK-200 unit) from the detector manufacturer Canberra is utilized in heating and controlling the temperature of the Ge crystals of the annealed detector. The vacuum inside the detector was maintained throughout the annealing process by constantly pumping the system using a turbo-molecular pumping station. The temperature of the germanium crystals, located inside a vacuum sealed chamber, of the detector and the vacuum level of this chamber were monitored throughout the annealing process, via both in-person observation and remote (online) monitoring. The Graphic User Interface (GUI) of an underlying LabVIEW script was utilized for running the monitoring process of the temperature and vacuum pressure values via a local network. To have the option of real-time online monitoring of the temperature, vacuum pressure, we coupled the web application Grafana with the Influx DB of the annealing data, as well as the backup time information of an Uninterruptible Power Supply (UPS) unit used in system.

X-ray spectroscopy station for sample characterization at ELI Beamlines

X-ray spectroscopy is a demanded tool across multiple user communities. Here we report on a new station for X-ray emission spectroscopy at the Extreme Light Infrastructure Beamlines Facility. The instrument utilizes the von Hamos geometry and works with a number of different sample types, notably including liquid systems. We demonstrate a simple and reliable method for source position control using two cameras. This approach addresses energy calibration dependence on sample position, which is a characteristic source of measurement uncertainty for wavelength dispersive spectrometers in XES arrangement. We also present a straightforward procedure for energy calibration of liquid and powder samples to a thin film reference. The developed instrumentation enabled us to perform the first experimental determination of the Kα lines of liquidized K3Fe(CN)6 as well as powdered and liquidized FeNH4(SO4)2. Finally, we report on proof-of-principle use of a colliding jet liquid sample delivery system in an XES experiment.

Neutron dose assessment in laser-generated ultra-short pulsed fields.

ELI Beamlines is one of the pillars of the Extreme Light Infrastructure European Research Infrastructure Consortium (ELI ERIC), the European project aiming at building the next generation of high power lasers for fundamental research and industrial applications. Several high-power lasers are hosted by the ELI Beamlines facility. Even at a power lower than the nominal one, when interacting with a target, the laser can generate mixed ionizing radiation fields of unique nature. One of the major laser systems, High-repetition-rate advanced petawatt laser system (HAPLS) was already used in commissioning experiments. Detecting the neutrons generated during these experiments has been a challenging task, since certain difficulties were faced. First, the experimental conditions were frequently altered during the commissioning phase (such as laser beam parameters, experimental geometry or target type). Next, the extremely short duration of the ionizing radiation pulse generated by the laser (~10-14s) complicated the correct interpretation of the data provided by the detectors designed and calibrated in standard fields. Here, one commissioning experiment is described, together with the means of addressing the problem of the detection of the ionizing radiation and the lessons learned in this endeavour.

Full aperture backscatter diagnostics for characterization of laser plasma instabilities at the extreme light infrastructure (ELI) beamlines.

We report on the commissioning of a full aperture backscatter diagnostics station for the kilojoule, nanosecond high repetition rate L4n laser operating at a wavelength of 527nm at the Extreme Light Infrastructure (ELI) - Beamlines, Dolni Brezany, Czech Republic. Light scattered back from laser-plasma interaction into the cone of the final focusing lens is captured and split into different channels to measure the signatures of laser plasma instabilities from stimulated Brillouin scattering, stimulated Raman scattering, and two plasmon decay with respect to back scattered energy, its spectrum, and its temporal profile. The performance was confirmed in a commissioning experiment with more than 800 shots at laser intensities ranging from 0.5 × 1013 to 1.1 × 1015Wcm-2. These diagnostics are permanently installed at ELI Beamlines, and can be used to understand the details of laser-plasma interactions in experiments with kJ and 527nm light. The large number of shots that can be collected in an experimental campaign will allow us to study the details of the laser-plasma interaction with a high level of confidence.

Nuclear photonics: Laser-driven nuclear physics

High-power lasers can produce high-energy gamma rays, charged particles, and neutrons and induce various types of nuclear reactions. In Extreme Light Infrastructure Nuclear Physics (ELI-NP), Romania, high-power lasers are entering a new realm of 10 PW peak power, capable of obtaining a focused intensity of 1023 Wcm–2. Such an intense laser pulse will be used for studies relevant to nuclear physics, high-field physics, and quantum electrodynamics, or the combination of laser gamma experiments. Here, we describe how a laser is used to drive high-energy photons and accelerate electrons and protons. These particles can be used for secondary interactions in nuclear physics. Laser-driven nuclear physics can be a source of nuclear isomers for applications in medicine and astrophysics.

Laser-driven muon production for material inspection and imaging

We numerically show that laser-wakefield accelerated electron beams obtained using a PetaWatt-scale laser system can produce high-flux sources of relativistic muons that are suitable for radiographic applications. Scalings of muon energy and flux with the properties of the wakefield electron beams are presented. Applying these results to the expected performance of the 10-PW class laser at the Extreme Light Infrastructure Nuclear Physics (ELI-NP) demonstrates that ultra-high power laser facilities currently in the commissioning phase can generate ultra-relativistic muon beams with more than 104 muons per shot reaching the detector plane. Simple magnetic beamlines are shown to be effective in separating the muons from noise, allowing for their detection using, for example, silicon-based detectors. It is shown that a laser facility like the one at ELI-NP can produce high-fidelity and spatially resolved muon radiographs of enclosed strategically sensitive materials in a matter of minutes.

XXII International Conference and School on Quantum Electronics: “Laser Physics and Applications”

The International School on Quantum Electronics “Laser Physics and Applications” was held for the first time as far back as 1980. Since then it has taken place biennially and has become an important international event in the field of laser physics and laser applications attracting participants from many countries, especially from south-eastern Europe. Traditionally, its program includes lectures delivered by prominent scientists dealing with investigations of basic physical phenomena, processes of interaction of laser radiation with matter and latest scientific results obtained in the research areas of quantum electronics and optics, as well as the technological practical applications of new ideas, devices, instruments and laser systems. Special attention is paid to the active participation of students and young scientists who have the opportunity to present their results and meet and share experience with outstanding professionals in their particular fields of research.The topics include the following:• Laser-matter interactions • Laser spectroscopy and metrology • Laser remote sensing and ecology • Lasers in biology and medicine • Laser systems and nonlinear optics • Alternative techniques for material synthesis and processing The 22nd edition of the ICSQE was held as a virtual forum due to the restrictions related to COVID-19 pandemic from September 19th to 23rd, 2022. The Institute of Electronics, Bulgarian Academy of Sciences, located in Sofia, Bulgaria, hosted the conference organization. The Big Blue Button on-line system was used as a technical platform for the meeting. The technical sessions of the International School on Quantum Electronics included 22 invited talks (30 min + 5 min Q&A), a Mini-Symposium “Extreme light infrastructure”, 11 oral contributions (30 min + 5 min Q&A) and in total 51 poster presentations divided into 5 sessions (1 hour each). The platform was available 24 hours, allowing discussions in addition to the technical program. The total number of participants was 90 from 16 countries.The XXII International Conference and School on Quantum Electronics: “Laser Physics and Applications” was held by the financial support from the Bulgarian National Science Fund under Project No. KP-06-MNF/4, 20.07.2022.List of Committees, International Advisory Committee, Program Committee, Local Organizing Committee, Lecturers, Oral Presentations, Poster Presentations are available in this pdf.

Spectrally tunable ultrashort monochromatized extreme ultraviolet pulses at 100 kHz

We present the experimental realization of spectrally tunable, ultrashort, quasi-monochromatic extreme ultraviolet (XUV) pulses generated at 100 kHz repetition rate in a user-oriented gas high harmonic generation beamline of the Extreme Light Infrastructure—Attosecond Light Pulse Source facility. Versatile spectral and temporal shaping of the XUV pulses is accomplished with a double-grating, time-delay compensated monochromator accommodating the two composing stages in a novel, asymmetrical geometry. This configuration supports the achievement of high monochromatic XUV flux (2.8 ± 0.9 × 1010 photons/s at 39.7 eV selected with 700 meV full width at half maximum bandwidth) combined with ultrashort pulse duration (4.0 ± 0.2 fs using 12.1 ± 0.6 fs driving pulses) and small spot size (sub-100 µm). Focusability, spectral bandwidth, and overall photon flux of the produced radiation were investigated, covering a wide range of instrumental configurations. Moreover, complete temporal (intensity and phase) characterization of the few-femtosecond monochromatic XUV pulses—a goal that is difficult to achieve by conventional reconstruction techniques—has been realized using a ptychographic algorithm on experimentally recorded XUV-infrared pump–probe traces. The presented results contribute to in situ, time-resolved experiments, accessing direct information on the electronic structure dynamics of novel target materials.

What can we learn from experiments with high-brilliance gamma beams?

An overview of the main directions of present-day studies with quasimonochromatic γ beams is presented with an emphasis on the research opportunities which will be provided to the users at the Extreme Light Infrastructure Nuclear Physics (ELI-NP) facility at Magurele near Bucharest. Experiments with γ beams at the extremes of high temperature and high neutron-to-proton ratios will be discussed. The opportunities for nuclear structure studies with γ rays with orbital angular momentum (OAM) are outlined and a few selected physics problems and classes of experiments, related to, e.g., changes of photonuclear cross sections in reactions with OAM photons, as well as the possibility to address nuclear excitations with higher multipolarity are discussed. The perspectives for studies of exotic nuclei within the Gamma Factory experiment at CERN are discussed, too.

Opening up high-performance laser science to the world at the extreme light infrastructure (ELI)

The Extreme Light Infrastructure (ELI) is a research facility that provides for a wide range of scientists access to the largest and most diverse set of high-performance laser systems in the world.

Zernike-coefficient extraction via helical beam reconstruction for optimization (ZEHBRO) in the far field

Abstract The spatial distribution of beams with orbital angular momentum in the far field is known to be extremely sensitive to angular aberrations, such as astigmatism, coma and trefoil. This poses a challenge for conventional beam optimization strategies when a homogeneous ring intensity is required for an application. We developed a novel approach for estimating the Zernike coefficients of low-order angular aberrations in the near field based solely on the analysis of the ring deformations in the far field. A fast, iterative reconstruction of the focal ring recreates the deformations and provides insight into the wavefront deformations in the near field without relying on conventional phase retrieval approaches. The output of our algorithm can be used to optimize the focal ring, as demonstrated experimentally at the 100 TW beamline at the Extreme Light Infrastructure - Nuclear Physics facility.

An interview with Vladimir Tikhonchuk

Vladimir Tikhonchuk, Professor Emeritus at Centre Lasers Intenses et Applications, University of Bordeaux, France, and senior researcher at the Extreme Light Infrastructure ERIC, ELI-Beamlines Facility, Czech Republic. His research is in the domain of high energy density physics and nonlinear optics, including inertial confinement fusion (ICF), dynamic processes in laboratory astrophysics, laser–plasma interactions, excitation of parametric instabilities, generation of magnetic and electric fields, acceleration of charged particles and energy transport.

Nuclear astrophysics studies with γ-ray beams: What do we expect to learn from them?

An overview of the main directions of present-day studies with quasimonochromatic γ beams is discussed with an emphasis on the research opportunities which will be offered at the Extreme Light Infrastructure Nuclear Physics (ELI-NP) facility at Magurele near Bucharest in Romania. Experiments with γ beams at the extremes of high temperatures are outlined, with an emphasis on prospective studies related to nuclear astrophysics and astroparticle physics. Some of the experimental setups for nuclear structure, reaction, and astrophysics studies, which are available at ELI-NP, are described.

Prospect for attosecond laser spectra of highly charged ions

The spectra of highly charged ions (HCIs) are of great significance for astronomical observation, astrophysical model establishment, and test of quantum electrodynamics (QED) theory. However, the transitions of HCI are mostly in the extreme ultraviolet or even X-ray range, the excitation spectra of HCI measured by laser spectroscopy in laboratory are very limited due to lack of the suitable light source. Up to now, only few experiments on the spectra of HCIs performed on synchrotron radiation, free electron laser or heavy-ions storage ring have been reported, which are summarized in this work. With the development of attosecond technology, several attosecond light source facilities have been built, such as extreme light infrastructure attosecond light pulse source (ELI-ALPS) and synergetic extreme condition user facility (SECUF), which have high photon energy and ultra-short pulse duration in the extreme ultraviolet and even soft X-ray range, providing new opportunities for laboratory research on HCI spectra and ultra short energy level lifetimes. Electron beam ion trap (EBIT), electron cyclotron resonance (ECR), and heavy-ion storage ring are usually used to generate ion target. But it is difficult to combine the attosecond laser source with large scale facility of HCI, for none of laboratories has both these two facilities now. Thus, two possible experimental schemes for attosecond spectrum of HCIs are proposed in this work. One scheme is that an EBIT can be designed as a terminal of attosecond laser facility, such as ELI-ALPS and SECUF, which can output different laser beams with high photon energy, ultra-short pulse duration or high flux. Another scheme is that a table-top HHG system pumped by an all-solid-state femtosecond laser or fiber femtosecond laser with high power can be combined with heavy-ion storage ring, such as ESR, CSRe, HIAF, and FAIR. Owing to high energy of ions in storage ring, the measurable energy levels of HCIs can even be extended to keV by the Doppler shift. Three different measurement methods: fluorescence detection, ion detection and attosecond absorption spectroscopy, can be used to obtain the HCI spectrum. Finally, a preliminary experimental setup for attosecond laser spectrum of HCI is proposed. The proposal on combining extreme ultraviolet attosecond light source with HCI target is discussed, and the feasibility of attosecond time-resolved precision spectrum for HCI is analyzed according to the typical parameters of attosecond light source and the known excitation cross-section and detection efficiency, which can provide a new platform for implementing ion level structure calculation, QED theory high-precision test and astronomical spectroscopic observation. It can be used to measure the ultra-short lifetime, low excitation cross-section ionic energy level, and even some transitions with large energy interval. We hope that this work can provide a reference for the experimental measuring of HCI spectrum and ion energy level lifetime in future.

Commissioning results from the high-repetition rate nanosecond-kilojoule laser beamline at the extreme light infrastructure

High-power laser–matter interaction and the related high-energy density physics (HEDP) are two important topics in modern physics. However, for decades, a very restrictive limitation prevents researchers from studying these topics efficiently: nanosecond-kilojoule class lasers are typically characterized by a low repetition rate (1 shot h−1) that restricts the data acquisition and limits the available statistics for analysis. Here, we describe the first results obtained using the high-repetition rate nanosecond-kilojoule (L4n laser beamline) experimental platform commissioned at the Extreme Light Infrastructure—Beamlines. We proved the capability to deliver hundreds of joules shots every three min with a very good repeatability. Using high-resolution x-ray spectroscopy, we studied highly resolved spectra of H-like and He-like Cl lines emitted from polyvinyl chloride targets and demonstrated that the plasma parameters (electron temperature and density) derived from the measured spectra are consistent with hydro-simulations. These results demonstrate the fulfillment of the designed platform performance which should become one of the most important assets for the HEDP community in the following decades.

Two-XUV-photon double ionization of neon

Two-XUV-photon double ionization of Ne, induced by an intense few-pulse attosecond train with a \ensuremath{\sim}4 fs envelope duration is investigated experimentally and theoretically. The experiment is performed at ELI-ALPS (Extreme Light Infrastructure Attosecond Light Pulse Source) utilizing the recently constructed 10 Hz gas phase high-order harmonic generation SYLOS GHHG-COMPACT beamline. A total pulse energy up to \ensuremath{\sim}1 \ensuremath{\mu}J generated in argon in conjunction with high-reflectivity optics in the XUV region allowed the observation of the doubly charged state of Ne induced by 40 eV central XUV-photon energies. The interaction of the intense attosecond pulse train with Ne is also theoretically studied via second-order time-dependent perturbation theory equations of motion. The results of this work, combined with the feasibility of conducting XUV-pump--XUV-probe experiments, constitute a powerful tool for many potential applications. Those include attosecond pulse metrology as well as time-resolved investigations of the dynamics underlying direct and sequential double ionization and their electron correlation effects.

Liquid nitrogen cooling, control and monitoring system for the ELIADE HPGe clover detectors at ELI-NP

We present a liquid nitrogen (LN2) cooling station for the high-purity germanium (HPGe) segmented clover detectors of the ELI-NP Array of DEtectors (ELIADE) spectrometer, including its associated filling control and monitoring systems, all designed and built in-house at Extreme Light Infrastructure - Nuclear Physics (ELI-NP), Măgurele, Romania. The automated LN2 filling process is controlled by a CompactRIO (cRIO) system from National Instruments through a custom LabVIEW software used for monitoring both the internal germanium crystal temperatures as well as the temperatures of external Pt100 sensors (used for detection of overflow of LN2 from detectors during a filling process). The detectors are filled with LN2 by opening their individual filling valves (which are mounted on the cooling station) and the process is automatically stopped once an overflow condition is fulfilled by the corresponding external Pt100 sensor located downstream. A twelve-hour cycle is used to periodically fill all of the detector dewars and keep their germanium crystals cool at all times. The associated Graphic User Interface (GUI), Command Line Interface (CLI) and Text User Interface (TUI) are used for both controlling and monitoring the above mentioned process. Alert and warning email messages were also enabled via the cRIO system so that users can be alerted in real-time in the event of any cooling malfunction. In this way, any issues related to the cyclic filling procedure, as well as any abnormal observations regarding the germanium crystal temperatures can be quickly and efficiently addressed before the detectors have a chance to warm back up to room temperature. Temperature data of all the Pt100 sensors corresponding to detectors as well as to the solenoid valves are made available in an influx database by the cRIO control system. The web application Grafana access the database and plots them in real-time for online monitoring.