Opening Words

• Sydney Gales
• Calin Alexandru Ur

Spatio-temporal profiles of Optics Lab, ELI-ALPS and ELI-NP lasers

• Maria Talposi (LSD)

Broadband laser pulses are often nonhomogeneous in space and time, leading to unwanted drops of intensity in the focal region. Characterizing and controlling their full spatio-temporal profile is a complex issue for large laser facilities. For this study, the INSIGHT scanning technique, that provides spectrally resolved wavefront measurements, was used in combination with a SPIDER device for spectral phase retrieval. Spatio-temporal profiles of a few femtosecond pulses at HPLS@ELI-NP, THz pump laser @ELI-ALPS, Sylos2@ELI-ALPS lasers and AVESTA@Optics Lab at ELI-NP have been measured. The comparison between their properties will be presented with emphasis on the capabilities and limitations of our INSIGHT instrument, such as pointing stability and bandwidth acceptance. An upgrade of the device is proposed.

100TW, 10Hz, 12 fs stable post compressed pulses at ELI-NP

• Gabriel Bleotu (LSD)

Self-phase modulation has been proposed and used to reduce the pulse duration for extreme light facilities, in the effort to go to Exawatt class lasers. We demonstrated an efficient and stable post-compression stage at the 100 TW, 10 Hz output of HPLS, using 1 J compressed pulses with initial 24 fs pulse duration. Various materials have been tested and the most appropriate ones have been used for an exhaustive characterization of post compressed laser pulses. We evaluate the spectral broadening effect in different glasses with respect to the focus quality, pulse duration, spectrally resolved spectra, temporal and spatial Strehl ratio, and for the first time, the spatio-temporal couplings of such broadband, ultra-intense laser pulses. We succeeded to reduce the actual pulse duration to 11.6 fs. This corresponds to an estimated factor of 1.5 net increase of the pulse peak power, after considering temporal Strehl and Fresnel energy loses.

Temporal drift suppression for the femtosecond-level synchronization of two ultrashort laser pulses from the 1 PW outputs of HPLS

• Andrei Naziru (LSD)

The architecture of the High Power Laser System from ELI-NP provides an unique-worldwide opportunity for synchronized dual-arm laser experiments such as non-linear Compton scattering, multiple stage electron acceleration and vacuum birefringence studies. The main challenges encountered in the experimental implementation is the in-situ measurement and stabilization of the femtosecond scale temporal jitter and drift of the laser pulses. In this work, a successful attempt of jitter measurement and drift suppression is presented. Based on an ultrafast optical switch and taking advantage of the identical dual arm laser configuration of the HPLS, the measurement technique shows promising experimental results, indicating a temporal jitter smaller than the pulse duration and the suppression of the temporal drift when a feedback loop using a precision delay line is closed.

Qualification of compressed helical pulses in PW-class laser systems

• Vicentiu Iancu (LSD)

Helical beams, produced by a spiral phase plate and passed through the pulse compressor, have been propagated over a distance of more than 40 m, without relay imaging, in the 100 TW experimental area, and also at the 1PW area E5. A doughnut shape was obtained in the focal plane, by optimizing the low-order distortions with a deformable mirror. Implementation of spectral filtering provided an explanation for imperfect singularity observed in the far field

On the injection, wave breaking and filamentation of electrons in LWFA

• Rares Iovanescu (LDED)

We study the origin of filamentation of the accelerated electrons in LWFA and their behavior in dependence to the plasma density. Several 2D PIC simulations were performed for different plasma densities, while keeping the other parameters constant. A filamentation is observed for lower plasma densities ~9*1017 cm-3 and a0>10 up to a limiting threshold density and then vanishes followed by the disappearance of the self-injection. Depending on the plasma density the bubble has a different dimension and shape, being bigger for lower densities. The filamentation appears when the bubble closes at its rear and depends on the closure angle of the bubble wall. If the angle is less than π, the filamentation does not set in from the beginning and is limited as the electron bunch is travelling towards the laser pulse. However, if the closure angle of the bubble wall exceeds π, which means that the wall edges turn towards the laser, the electron bunch travels inside the bubble and forms the filaments. This is related to the fact that the constant phase surface of a broken wave in plasma follows such curves that close differently at the rear of the bubble. We present the energy distribution for the different plasma density and the evolution of the filaments in time. Besides, we measure the maximum electron energy for each plasma density at intervals of 250 fs, and obtain lower values in the cases with filamentation.

An improved ion acceleration scheme with high intensity laser-generated surface plasma waves

• Bogdan Corobean (LDED)

In certain configurations, surface plasmons (SPs) can be generated as a result of the interaction between a laser pulse and a target. By taking advantage of this process, it has recently been shown that the properties of properties of accelerated ions can be greatly improved, compared to more widely-used methods, such as TNSA. We have performed a series of simulation using the particle-in-cell (PIC) using the code SMILEI in order to verify the effects of the pre-plasma scale length has on the properties of the accelerated particles (in particular the peak energies obtained). We have also performed converge tests with the aim of finding the optimal numerical parameters for such simulations.

Shadowgraphy based diagnostics for high power lasers experiments

• Alexandru Magureanu (LDED)

Shadowgraphy based diagnostics are powerful tools in high-power laser-driven experiments that provide real-time information about the interaction. In this work, we describe the design of a shadowgraphy system equipped with either a standard CCD camera or a wavefront sensor camera. We also report on the results attained during the commissioning campaign of the 1 PW laser of the ELI-NP facility [1]. The 1 PW laser system has a maximum beam energy of 24 J, with pulse duration and central wavelength of 24 fs and 810 nm, respectively [2]. The shadowgraphy was performed by using a probe beam with the fundamental wavelength of the laser and synchronizing it with the main laser beam. This technique was used for imaging the interaction of the focused laser beam with either a solid target or a gas cell target. The shadowgraphy with the wavefront sensor was employed with gas targets, in the laser-driven electron acceleration experiment, to measure the phase change of the wavefront of the probe beam after passing throughout the plasma channel generated during the acceleration process. This wavefront modification provides information about the electron plasma density. The standard shadowgraphy was used with solid targets during the TNSA experiment to attain information about the laser temporal contrast by looking at pre-plasma signature in the interaction. [1] K. A. Tanaka, K. M. Spohr, D. L. Balabanski et all, Current status and highlights of the ELI-NP research program. Matter and Radiation at Extremes vol.5, p. 024402 (2020) [2] F. Lureau, G. Matras, O. Chalus et all, High-Energy Hybrid Femtosecond Laser System Demonstrating 2 × 10 PW Capability, High Power Laser Science and Engineering, vol.5, p. e43 (2020)

Computer Vision Applications for the ELI-NP High Power Laser System (HPLS) with Convolutional Neural Networks (CNNs).

• Vlad Gaciu (LDED)

The High Power Laser System (HPLS) at ELI-NP has already collected and stored large amounts of data pertaining to significant individual characteristics of the system, some of which can now be used for automation processes with computer vision. The process of utilizing image processing and Convolutional Neural Network (CNN) classification techniques can extract valuable information from tens of thousands of Near-Field and Far-Field wavefront images taken by CCD cameras, reducing the time taken to acquire such information from hours or days down to seconds or minutes. This work is also a first step towards automating the alignment calibration of the most powerful laser in the world with peak power laser pulses of 10.2 PW.

Backreflection monitoring system for HPLS

• Dmitrii Nistor (LSD)

Laser driven experiments are being conducted with world’s most powerful laser at ELI-NP to perform well-controlled studies of relativistic laser-plasma interaction. During 1 PW experimental campaign, noticeable degradation of optical components located at the entrance of the first amplifier was observed; as thorough investigations yield us, laser- matter interaction can generate back-reflected coherent light which may travel upstream from the experimental area, through the beam transport, optical compressor and several stages of amplification (usually with residual gain still present in the crystals) and can pose significant risk to the laser system by damaging unique and expensive optical components. This presentation aims to show a diagnostic system consisting of an adjustable imaging, Near-Field and Far-Field, spectrometer and a photodiode designed to investigate further the generation and optical properties of back-reflected light such as: energy levels, beam profile, direction of propagation and spectrum. The optical design was done through an in-house built ABCD formalism software and the mechanical design with SolidWorks CAD software. The device was installed in HPLS and test signals were monitored during the beamtime at the end of 2022 and no further damage was recorded to date in order to commission the system.

Microfluidics for high power laser metrology

• Stefan Popa (LSD)

With laser developments aimed towards increasing the peak power available, the field of high power laser metrology is facing the challenge of accurately measuring laser beams over a wide range of intensities. Traditional methods of beam sampling often lead to distortions of the beam quality, making accurate measurement difficult. However, advancements in microfluidics have opened up new possibilities for direct measurement at high intensities. Microfluidic media can provide a powerful tool for direct measurement of laser beams at high intensity and high repetition rate due to their regenerative nature. A thin liquid sheet formed from two impinging micrometer scale jets has been successfully used to characterise the spectral phase of the 1PW output of the High Power Laser System at ELI-NP. This presentation describes the liquid sheet implementation for the spectral phase measurement of pulses far from the Fourier transform limited pulse duration along with a characterisation of the liquid sheet geometry and stability. Besides their use in laser metrology, the controllable thickness profile and good stability make liquid sheets a suitable candidate for laser targets for ion acceleration, with refresh rates in the 10 Hz range.

Towards 100 nanometer Thick Laser Targets: Increasing the Exfoliation Efficiency of the Graphite Layers through the Control of the sp2/sp3 Hybridization Ratio of the Precursors

• Cosmin Jalba (LSD)

The aim of this work is highlighting the importance of precursors’ choice for the efficiency of graphite layer exfoliation process. X-ray Photoelectron Spectroscopy allowed the identification of the compositional structures, showing the carbon sp2 and sp3 hybridisation separation in the photoemission spectra, while Scanning Electron Microscopy/Energy-dispersive X-ray Spectroscopy provided 2D surface morphology and chemical composition. One-step synthesis of graphite intercalated compound (GIC) was successfully used for sample expansion and exfoliation processes (under ambient conditions), using H2SO4 as intercalant and H2O2 as reactive specie. The results showed that the graphite precursor containing the majority sp2 hybridization type can be easily exfoliated.

HPLS field equipment for ACIS

• Adrian Toader (LSD)

The interlock of a laser is a mechanism which can contribute to laser safety by automatically turning off the laser or by blocking a laser beam via a beam blocker. An existing HPLS interlock system was delivered by the HPLS supplier. It is composed of HPLS interlock boxes and emergency buttons which enables/disables the class IV lasers using shutters and power supplies inhibition.The safe operation of the ELI-NP facility from the radiological protection perspective is covered by the Radiation Safety Strategy (RSS), a strategy that has the main objective of ensuring that all the activities proposed for the implementation can be carried out safely from radioprotection point of view. Thus, the ACIS (Access control and interlock system is directly related to Radiation Safety Strategy as it is intended to prevent any unauthorized or accidental entry into experimental areas.The presentation intends to show the entire wiring network for HPLS, including other additional systems (like configurator box, gate valve monitoring system, attenuators position monitoring systems), which are connected at ACIS. ACIS interfaces with few systems like HPLS configurator box (which give us the laser configuration :100 TW, 1 PW or 10 PW for each arm), with gatevalves (part of the vacuum system of HPLS) which can allow the laser beam towards the experimental areas, and also with laser attenuators installed on each arm of HPLS in order to send the align beam (at required laser energy) towards experimental areas. The network which was installed is modular and gather all the required laser signals for ACIS in the same place.

Study of nuclei relevant to ELI-NP projects using Large Scale Shell Model code NuShellX

• Emanuela Boicu (GDED)

Large Scale Shell Model was used to study nuclei from different mass regions related to ELI-NP and IFIN experiments. 2+ energy levels and reduced transition probabilities from ground state to the first 2+ state, using different effective interactions, were calculated. The parameters used in the computation were optimized to best reproduce experimental data available for the nuclei studied.

RF Linac Design Modelling for Optimization of Beam Parameters for ICS γ-ray Source System

• Emilian Iuciuc (GSD)

High brightness beams are desired for application to Inverse Compton Scattering systems for generation of high-quality x- and γ-rays. They bring new opportunities for nuclear physics research. In the ICS mechanism high energy electron is interacting with photon. It results in scattered photon with high energy. Results from computer simulations made on the electron beam will be presented. Different configurations of a radio-frequency injector were analyzed. The rf injector consists of a photocathode rf electron source with magnetic devices, and a standing wave cavity for an initial particle acceleration. Then the beam is accelerated and gains relativistic energy in a radio-frequency linear accelerator. Electron beam parameters were investigated with use of the computer program for tracking a particle beam through defined external electric and magnetic fields. Because a cross-section of a collision between electron and photon beam is very low, the high brightness electron beam is crucial specification for the gamma beam systems. The beam parameters of interest are emittance, beam spot size, average energy, energy spread, electron bunch length, and Twiss parameters. Beam density, number of particles in bunch, must find good compromise between an optimum necessary for creation of high-performance γ-rays, and a limit in available technology.

Optimal sensitivity of the Mach-Zehnder interferometer with detection strategies

• Karunesh Kumar Mishra (LGED)

Quantum metrology provides a means of circumventing practical constraints in sensing devices. It is especially relevant to the detection of gravitational radiation in projects like LIGO [1] or the Virgo[2] interferometer, where high-precision measurements of the relative distance between two widely separated masses are required. An optical interferometer can be used to precisely measure the phase shift. The phase sensitivity of a Mach-Zehnder interferometer (MZI) depends on a number of factors, such as the input state, the beam splitters’ transmission coefficients, and the employed detection schemes. Among these detection schemes we will discuss the single-, difference-intensity mode, the balanced homodyne, and the parity detection schemes [3, 4]. We will outline the method to compute both the optimal working point and the peak phase sensitivity for each of the aforementioned detection schemes.

Discovering Magnetic Resonance Biomarkers for Irradiated Cells

• Diana Serafin (LGED)

In the recent use of radiotherapy to treat and control various types of cancer, dose-rates are explored to minimize radiation toxicity. Molecular biomarkers evaluated via in-cell studies have the potential of monitoring the radiation dose and dose-rate response within a biologically relevant time-window of up to tens of hours. We investigate the metabolic changes induced by radiation in cells via Magnetic Resonance Spectroscopy. The presentation will detail procedures used for metabolic imaging of radiation effects in glioblastoma U251 MG cell cultures. The specific investigation of metabolic pathways using carbon-13 isotopically-enriched glucose will be discussed. References M-C Vozenin, J. H. Hendry , C.L. Limoli, Biological Benefits of Ultra-high Dose Rate FLASH Radiotherapy: Sleepy Beauty Awoken https://pubmed.ncbi.nlm.nih.gov/31010708/ Undurti N. Das, Molecular Biochemical Apects of Cancer

Physics opportunities for radioactive ions studies at the Gamma Factory

• Dragos Nichita (GDED)

The study of radioactive ions, far away from stability, has offered the opportunity to test nuclear structure models as well as important astrophysical theories. The newly proposed radioactive ion beam facility [1] at the Gamma Factory [2] can produce and extract radioactive ions with yields that permit the measurement and analysis of new, rare isotopes for a wide range of elements with excellent coverage of both N = 50 and N = 82 r-process waiting points. 1. D. Nichita et al., Ann. der Phys. 534 (3), 2022; 2. M.W. Krasny et al., ArXiv 1511.07794, 2015;

Study of neutron production in 19F(alpha,n) reaction

• Roy Rajat (GDED)

Fluorine compounds of U and Pu are ubiquitous in the nuclear fuel cycle. The 19F(α, n) reaction, induced by the spontaneous fission of alpha (3-6 MeV), results in a neutron yield important for the fabrication or storage of nuclear reactor fuel. The 19F(α,n) yield varies rapidly in the energy range of emitted alpha-particles (3-6 MeV). The neutron flux from this reaction as well as prompt fission neutrons should be accordingly considered in the safeguard applications. The underlying experimental cross-section of 19F(α,n) reactions is one of the main source of uncertainty to design a proper shielding for the fuel rods. In our experiment we measured 19F(α,n) cross-section in the 3-7 MeV energy region. The α-beam was provided by the 3 MV Tandem accelerator of IFIN-HH and delivered to the 19F target installed at the centre of ELIGANT-TN detector array. The ELIGANT-TN is a state-of-the-art long (3He) neutron counter, which provides flat-efficiency at a level of 37%. In my presentation the details of the experiment and the results of the preliminary analysis are reported.

Direct measurement of the 19F(p,α)16O reaction

• Teodora Madgearu (GDED)

The 19F(p,α)16O reaction is important for understanding the fluorine abundance in the outer layers of asymptotic giant branch (AGB) stars and it might also play a role in hydrogen-deficient post-AGB star nucleosynthesis. Up to now, theoretical models overproduce F abundances in AGB stars with respect to the observed values, thus calling for further investigation of the reactions involving fluorine. Indeed, in the last years, new direct and indirect measurements improved significantly the knowledge of the 19F(p,α0)16O cross section at deeply sub-Coulomb energies (below 0.8 MeV). Nevertheless, those data are larger by a factor of about 1.4 with respect to the previous data reported in the NACRE compilation in the energy region 0.6-0.8 MeV. In order to solve these discrepancies we present here a direct experiment performed at INFN-LNS using a silicon strip detector array (LHASA - Large High-resolution Array of Silicon for Astrophysics). Our results clearly confirm the trend of the latest experimental data in the energy region of interest. The 19F(p,α)16O reaction rate is the sum over the (p,α0), (p,απ) and the (p,αγ) channels. While the (p,α0) rate is well constrained by the present existing data, down to the lowest energies, almost nothing is known from experiments on the (p,απ) and (p,αγ) rates. Despite its importance, the S-factors and the branching ratio between the α0, απ and αγ outgoing channels in the 19F(p,α)16O reaction are still largely uncertain at astrophysical energies, emphasizing the need for better measurements. Thus, a direct measurement using the new detector, ELISSA (Extreme Light Infrastructure – Silicon Strip Array), coupled with LHASA will be performed in September 2022 at IFIN-HH. This setup is allowing us to discriminate the (p,απ) and (p,αγ) reaction rates at very low energies

Nuclear structure studies with high-precision mass measurements of spontaneous fission fragments at the FRS-Ion Catcher

• Anamaria Spataru (GDED)

Nuclear masses are a basic property of the nuclei, which reflect information on their structure. The transition between the spherical and deformed nuclear shapes, known as shape transition, is observed through the evolution of the two neutron separation energy (S2n) and its first derivative (dS2n). Deviations from linear decrease of the S2n and dS2n parameters are indicating a possible shape transition. The results presented in this contribution are part of an experimental campaign that took place at the FRS-IC at GSI. Here, accurate mass measurements of spontaneous fission fragments at N=90 are measured using time-of-flight technique and used in the calculations of their S2n and dS2n values. The measured mass values are compared with the literature and the calculated S2n and dS2n with theoretical calculations.