The following section presents scientific highlights and news that resulted from in-house and/or collaborative activities of ELI-NP researchers, leveraging the unique ELI-NP equipment and capability that is developed in the ramp up phase towards full operation, and state of the art facilities worldwide.
Influence of spatio-temporal couplings on focused optical vortices

Photonics 9(6), 389
(Published on May 2022)

Photonics Magazine recently published an article by our colleagues: Ana-Maria Talposi, Vicentiu Iancu and Daniel Ursescu, scientific researchers at ELI-NP entitled: "Influence of Spatio-Temporal Couplings on Focused Optical Vortices". The article addresses for the first time in a systematic manner the combined contribution of the spatio-temporal distortions in ultrashort pulses and helical wavefront. It points out the rotation of the singularity in the optical vortex in the presence of the spatial chirp, angular chirp and pulse front tilt.

Symmetry versus entropy: Long-lived states and coherences

Progress in Nuclear Magnetic Resonance Spectroscopy, Volume 122
(Published on February 2021)

Applications of long-lived nuclear states in magnetic resonance to the study of biomarkers, protein structure, imaging, and metabolomics are presented. Recently-invented molecular symmetry-based approaches for magnetic resonance have implications that are significant for molecular imaging via magnetic resonance, in vitro as well as in vivo, for quantum computing and for other fields.

Spin states that are resilient to relaxation mechanisms became available in molecules of different sizes and structures, as experimental developments broadened the scope of symmetry-adapted spin states.
Electron transport in a nanowire irradiated by an intense laser pulse

Physical Review Research 3, 033262
(Published on 17 September 2021)

The interactions of ultra-intense lasers with solid targets with nanowires received a lot of attention because they appear to show potentials to increase the laser light absorption rate. Laser-nanowire interactions open up various applications such as attosecond bunch generation, enhanced x-ray generation, brilliance gamma-ray yield, as well as efficient micro fusion. Many studies have experimentally shown enhanced laser energy absorption on a solid target covered by nanowires. The absorption mechanism at the nanoscale is not fully understood and exhibits a distinct behavior following the irradiation of an intense laser pulse.

Ultrafast olivine-ringwoodite transformation during shock compression

Nature Communications, 12:4305
(Published on 14 July 2021)

Meteorites from interplanetary space often include high-pressure polymorphs of their constituent minerals, which provide records of past hypervelocity collisions. These collisions were expected to occur between kilometre-sized asteroids, generating transient highpressure states lasting for several seconds to facilitate mineral transformations across the relevant phase boundaries. However, their mechanisms in such a short timescale were never experimentally evaluated and remained speculative.

Nuclear resonance fuorescence drug inspection

Scientific Reports volume 11, Article number: 1306
(Published 14 January 2021)

This study is a simulation work to explore the drug inspection based on the laser-Compton scattering (LCS) γ-ray source, for example the variable energy Gamma (VEGA) system at ELI-NP.

In the present study, combining nuclear resonance fluorescence (NRF) spectroscopy and the element (or isotope) ratio approach, a novel inspection method that can simultaneously reveal the elemental (or isotopic) composition of the illicit drugs, such as widely abused methamphetamine, cocaine, heroin, ketamine and morphine, is presented. In the NRF spectroscopy, the nuclei are excited by the induced photon beam from the LCS γ-ray source, and the measurement of the characteristic energies of the emitted γ-ray from the distinct energy levels in the excited nuclei provides "fingerprints" of the interested elements in the illicit drugs. The element ratio approach is further used to identify drug elemental composition.

Angular momentum generation in nuclear fission

Nature volume 590, pages 566–570
(Published 24 February 2021)

Nuclear physicists at the ELI-NP have contributed to an international research collaboration to determine how the spin of the two fragments, resulting from the splitting of an atomic nucleus, is generated and published their findings in Nature.
Despite the process being known for a long time, one of the open questions about the process remaining to this day is why, when a heavy atomic nucleus fissions, the resulting fragments are observed to emerge spinning, even when the original nucleus did not spin at all. There are many competing theories, but the majority state that the spin of the fission fragments is generated before the nucleus splits, leading to a clear correlation of the spins of the two partner fragments.

Accessing the Single-Particle Structure of the Pygmy Dipole Resonance in 208Pb

Physical Review Letters 125, 102503
(Published 02 September 2020)

The new findings come from an international collaboration led by nuclear experimentalist Dr. M. Spieker (Florida State University, USA). The novel data were collected from (d,p) and resonant proton scattering experiments performed at the Q3D spectrograph of the Maier-Leibnitz Laboratory in Garching, Germany.

The theoretical work was carried out by nuclear theorists Dr. N. Tsoneva (ELI-NP), a recognized expert in energy-density functional and quasiparticle-phonon model theory (EDF+QPM), and Prof. B. A. Brown (Michigan State University, USA), a world leader in large-scale nuclear shell model (LSSM).

The emission of collimated γ-ray beams from structured laser-irradiated targets with a prefilled cylindrical channel and its scaling with laser power (in the multi-PW range) is examined using three-dimensional kinetic simulations. The laser power is increased by increasing the laser energy and the size of the focal spot while keeping the peak intensity fixed at 5×1022 W/cm2.

(a) Schematic setup for generation of a directed γ-ray beam from a laser-irradiated structured target
Enhancement of laser focused intensity greater than 10 times through a re-entrant cone in the petawatt regime

Optics Letters Vol. 45, Issue 13, pp. 3454-3457
(Published 16 June 2020)

A simple method to amplify the laser pulse intensity by an order of magnitude from 8x1020 W/cm2 using a plastic re-entrant micro-cone target is proposed. We found an increase of the initial laser pulse intensity by more than 10 times for a micro-cone tip diameter of 5 μm upon performing two-dimensional particle-in-cell simulations.

Disentangeling the properties of the exotic double-gamma nuclear decay

Nature Communications vol. 11, Art. nb: 3242
(Published on 26 June 2020)

The exotic decay studied is a very rarely occurring type of decay in which a radioactive quantum state of an atomic nucleus, instead of decaying directly to a lower energy state with the emission of a single gamma-ray, emits two gamma rays and changes to an energetically lower state via a quantum double-leap through a virtual coupling to a higher-energy state. Such second-order double-decays are a unique consequence of quantum mechanics, first predicted in the doctoral dissertation of Nobel laureate Maria Göppert-Meyer under the supervision of Max Born in Göttingen University in 1931.

In this particular case, both single and double decays are allowed. Thus, this rare process is therefore called competitive double gamma decay by the scientists and is designated with the symbol "γγ/γ". On October 15, 2015, a team of nuclear physicists from Technische Universität Darmstadt announced the discovery of this process in the Ba-137 nuclide in the magazine Nature, showing that this process only occurs there with a probability of around two double-decays per one million single-decays.

Our international team, led by Julien Fuchs (LULI, France) and Sophia Chen (ELI-NP), carried out an experiment at Lawrence Livermore National Laboratory (USA) using two high-intensity short pulse laser beams: a first beam drives a broadband proton beam from a first target to probe the magnetic fields created in a second target irradiated by a second beam. We observed that the fields related to instability could be measured quite easily and that they existed over much longer than expected. It then took several years of theoretical and numerical effort, led by Laurent Gremillet et Charles Ruyer (CEA, France), using the advanced simulation codes and supercomputers to model the data (see Figure). In doing so, two variants of Weibel's instability were identified depending on the region of the plasma, namely the collisionless electromagnetic modulations can be measured as the energetic electrons traversed the dense center region and later the lower density coronal regions.

Photodisintegration of Li-7 measured by ELI-NP team

Physical Review C 101, 055801
(Published 14 May 2020)

One of the unresolved questions in nuclear astrophysics is the so-called "cosmological Lithium problem". Lithium isotopes are produced during the first 15 minutes after the Big Bang, the initial event that created the Universe. Big-Bang Nucleosynthesis (BBN) is the theory that predicts the abundances of light elements at the beginning of the Universe based on the cross sections of nuclear reactions. While for all the light elements there is a good agreement between observed and calculated primordial abundances, for Li-7 there is a discrepancy of a factor of 3-4.

Silicon array from Oak Ridge National Laboratory in USA for detecting the 4He and 3H particles from the photodisintegration of 7Li experiment at HIγS

The Charged Particle Detection group at ELI-NP proposed the measurement of the photodisintegration cross section of 7Li through the 7Li(γ,3H)4He reaction as one of the first experiments to be performed at ELI-NP using the γ-ray beam and the ELISSA detector array. However, before the ELI-NP facilities and detectors are implemented, a proof-of-principle proposal was initiated to measure the 7Li(γ,3H)4He reaction at HIγS.

Direct observation of imploded core heating via fast electrons with super-penetration scheme

Nature Communications, 10, Article number 5614
(Published 09 December 2019)

One of the promising approaches to ignite high density imploded fusion fuel (DD or DT) is fast ignition in inertial confinement laser fusion that separates the laser systems one for imploding the fuel shell to a high density and another for igniting the highly compressed core. We have tested so called "super-penetration mode" where a self-focusing fast heating beam penetrates the large corona plasma surrounding the compressed core and to heat the core via. fast electrons. Time sequences of the heating is clearly shown here. Our study indicates that the energy coupling efficiency can be improved up to 12% by optimizing the key factors in future ignition-scale plasmas.

Cu-Ka image (8 keV) with the different injection timing of fast heating laser pulse (LFEX) at 2.2, 2.6 and 4.6 nsec. Compressed core shows the time sequence of the heating by fast electrons.