Study of the laser-driven ion acceleration in the relativistically induced transparency regime using ultra-thin foils and cryogenic targets
Laser-driven ion acceleration (LDIA) presents a compact and cost-effective alternative to traditional particle accelerators. Recent developments have enabled proton energies up to 160 MeV using ultra-thin foil targets irradiated by ultra-intense laser pulses, exploiting relativistic transparency regimes. This regime occurs when the laser pulse penetrates a near-critical plasma, generated by tailoring target thickness to the laser parameters, enabling multi-stage acceleration and enhancing proton energies without the need for contrast-enhancing techniques like plasma mirrors. This PhD project aims to further optimize proton acceleration in the transparency regime, with the goal of achieving 200 MeV energies using high-repetition-rate laser systems.
The first phase involves 3D Particle-In-Cell (PIC) simulations with Smilei, focusing on the sensitivity of laser-target interaction to temporal laser profiles for robust acceleration. The second phase investigates cryogenic hydrogen ribbon targets, developed by CEA, as an alternative to solid foils. These targets are near-critical in density, tunable in thickness, and compatible with high-repetition-rate operation, while providing mono-species proton beams. Experimental work will be conducted in collaboration with LULI and CEA, with preparations for experiments at the Apollon facility.
Plasma Mirrors Towards Extreme Intensity Light Sources and High-Quality Compact Electron Accelerators
The research programs conducted at the Lasers Interactions and Dynamics Laboratory of the French Atomic Energy Commission (CEA) aim to understand the fundamental processes involved in light-matter interactions and their applications. As part of the CEA-LIDYL, the Physics at High Intensity (PHI) group conducts studies of laser-matter interactions at extreme intensities, for which matter turns into an ultra-relativistic plasma. Using theory, simulations and experiments, researchers develop and test new concepts to control the laser-plasma interaction with the aim to produce novel relativistic electron and X-UV attosecond light sources, with potential applications to fundamental research, medicine and industry.
In collaboration with the Lawrence Berkeley National Laboratory, the group is a core developer of the exascale Particle-In-Cell (PIC) codes WarpX/PICSAR for the high-fidelity modelling of laser-matter interactions. It also pioneered the study and control of remarkable optical components called ‘plasma mirrors’, which can be obtained upon focusing a high-power laser with high-contrast on an initially solid target. In the past five years, the PHI group has developed two concepts exploiting plasma mirrors to manipulate extreme light for pushing the frontiers of high-field science. The first concept uses relativistic plasma mirrors to amplify the intensity of existing lasers by orders of magnitude and probe novel regimes of Strong-Field Quantum Electrodynamics (SF-QED). The second uses plasma mirrors as high-charge injectors to level up the charge produced in laser-plasma accelerators (LPAs) to enable their use for medical studies, industrial applications and fundamental research (collider design, electron-laser collisions for SF-QED studies).
In this context, the PhD candidate will first improve our simulation tool WarpX to speed-up plasma mirror simulations. They will then use WarpX to optimize the use of plasma mirrors as intensity boosters for the study of SF-QED. In collaboration with Brigitte Cros's team at CNRS and within the framework of novel collider designs based on Laser-Plasma Accelerators (LPAs), the PhD candidate will finally investigate and optimize the use of plasma mirrors as optical components for the coupling of multiple LPA stages. This will be crucial for developing compact acceleration schemes that can be scaled to produce high-energy, high-quality electron beams.
VHEE Radiotherapy with Electron Beams from a Laser-Plasma Accelerator
The research programs conducted at the Lasers Interations and Dynamics Laboratory of the French Atomic Energy Commission (CEA) aim to understand the fundamental processes involved in light-matter interactions and their applications. As part of the CEA-LIDYL, the Physics at High Intensity (PHI) group conducts studies of laser-matter interactions at extreme intensities, for which matter turns into an ultra-relativistic plasma. Using theory, simulations and experiments, researchers develop and test new concepts to control the laser-plasma interaction with the aim of producing novel relativistic electron and X-UV attosecond light sources, with potential applications to fundamental research, medicine and industry.
In collaboration with the Lawrence Berkeley National Laboratory, the group strongly contributes to the development of the code WarpX used for the high-fidelity modelling of laser-maIer interactuons. It also pioneered the study and control of remarkable optical components called ‘plasma mirrors’, which can be obtained by focusing a high-power laser with high contrast on an initially solid target. In the past five years, the PHI group has developed core concepts exploiting plasma mirrors to manipulate extreme light for pushing the frontiers of high-field Science. One of these concepts uses plasma mirrors as high-charge injectors to level up the charge produced in laser-plasma accelerators (LPAs) to enable their use for medical studies such very high energy electrons (VHEE) radiotherapy. This concept is being implemented at CEA on the UHI100 100 TW laser facility in 2025 to deliver 100 MeV - 200 MeV electron beams with 100 pC charge/bunch for the study of high-dose rate deposition of VHEE electrons on biological samples.
In this context, the PhD candidate will use our simulation tool WarpX to optimize the properties of the electron beam produced by LPAs for VHEE studies (electron beam quality and final energy). He/She will then study how the LPA electron beam deposits its energy in water samples (as biological medium) using Geant4. This will help assessing dose deposition at ultra-high dose rate and develop novel dosimetry techniques for VHEE LPA electron beams. Finally, the Reactive Oxygen Species (ROS) production and fate in water will be studied using the Geant4-DNA toolkit. This module has mainly data tabulated at electron energies below 10 MeV and will therefore require measures cross-section of water-ionization processes from experiments at 100 MeV. This will be performed on the UHI100 100 TW laser by the DICO group of the CEA-LIDYL, in collaboration with the PHI group.
Ultrafast spin currents and ferroic oxides
This PhD thesis lies at the intersection of ultrafast spintronics and the physics of spin currents on sub-picosecond timescales. Pure spin currents are currently attracting considerable attention due to their central role in the development of next-generation spintronic devices. As data consumption continues to grow exponentially, information and communication technologies must process increasingly large volumes at higher speeds, all while minimizing energy consumption. In this context, ultrafast information processing has become a major challenge.
Pure spin currents offer several decisive advantages: in addition to their dissipationless propagation, they can now be generated, transmitted, and detected on timescales of just a few hundred femtoseconds. This progress paves the way for the emergence of ultrafast spintronic components and devices operating in the terahertz range.
The aim of this thesis project is to investigate the fundamental mechanisms governing the generation and propagation of pure spin currents on picosecond and sub-picosecond timescales, with a particular focus on ferroic oxides. These materials exhibit a wide range of remarkable and tunable properties, making them ideal candidates for enabling ultrafast spin current functionalities and addressing the societal challenges of tomorrow.
The core of this thesis work will involve the implementation of time-resolved optical and magneto-optical techniques to probe the ultrafast magnetic dynamics in epitaxial thin films of ferromagnetic and antiferromagnetic oxides. The main expected outcomes include overcoming key bottlenecks: on one hand, the tunability of ultrafast spin current generation through the half-metallicity of selected ferromagnetic oxides; and on the other hand, the control of spin information propagation at terahertz frequencies in antiferromagnetic oxides.
Hemoglobin S polymerization and diffusion in different hemoglobin mixtures HbYxHbS(1-x) with Y=At, A0, F…
Sickle cell disease (SCD) is a genetic disorder of the blood, causing anemia. It results from the polymerization of a mutated hemoglobin HbS, the oxygen-carrying protein found in red blood cells (RBCs), which causes the soft cells to deform into a rigid sickle shape under certain circumstances. Because the deformed cells induced by the polymerization will clog the blood capillaries, it induces an increase in blood pressure and ultimately degeneration of the various organs. Pharmacological treatments for sickle cell anemia include hydroxyurea, a molecule that promotes the synthesis of fetal hemoglobin (HbF) which leads to a mixture of hemoglobin HbFxHbS(1-x) in the blood, with HbF partially inhibiting polymerization of HbS. Gene therapy is also used for the treatment of this disease by stimulating the production of therapeutic hemoglobin (HbAt), or normal hemoglobin (HbA0). In collaboration with the Department of Genetic Diseases of the Red Blood Cell at Henri-Mondor hospital, we propose to study the effect of the addition of different types of hemoglobin on the polymerization process as well as the kinetics of oxygen capture at RBC level. This model study is directly linked to the treatments developed to cure this disease and aim to try to better understand them from a molecular point of view.
Measuring quantum decoherence and entanglement in attosecond photoemission
The PhD project is centered on the advanced study of attosecond photoemission dynamics. The objective is to access in real time decoherence processes induced, e.g., by electron-ion quantum entanglement. To that aim, the young researcher will develop attosecond spectroscopy techniques making use of a new high repetition rate Ytterbium laser.
Detailed summary :
In recent years, there has been spectacular progress in the generation of attosecond (1 as=10-18 s) pulses, awarded the 2023 Nobel Prize [1]. These ultrashort pulses are generated from the strong nonlinear interaction of short intense laser pulses with gas jets [2]. They have opened new prospects for the exploration of matter at the electron intrinsic timescale. Attosecond spectroscopy allows studying in real time the quantum process of photoemission and shooting the 3D movie of the electron wavepacket ejection [3, 4]. However, these studies were confined to fully coherent dynamics by the lack of experimental and theoretical tools to deal with decoherence and quantum entanglement. Recently, two techniques have been proposed to perform a quantum tomography of the photoelectron in its final asymptotic state [5, 6].
The objective of the PhD project is to develop attosecond spectroscopy to access the full time evolution of decoherence and entanglement during the photoemission process. Quantum tomographic techniques will be implemented on the ATTOLab laser platform (https://iramis.cea.fr/en/lidyl/atto/attolab-platform/) using a new Ytterbium laser source. This novel laser technology is emerging, with stability 5 times higher and repetition rate 10 times higher than the current Titanium:Sapphire technology. These new capabilities represent a breakthrough for the field and allow, e.g., charged particle coincidence techniques, to study the dynamics of photoemission and quantum entanglement with unprecedented precision.
This PhD project is performed in the frame of a recently funded European Network QU-ATTO (https://quatto.eu/), providing an advanced training to 15 young researchers, and opening many opportunities of joint work with European laboratories. In particular, strong collaborations are already ongoing with the groups of Prof. Anne L’Huillier in Lund, and Prof. Giuseppe Sansone in Freiburg. Due to the Mobility Rule, candidates must not have resided (work, studies) in France for more than 12 months since August 2022.
The student will receive solid training in ultrafast optics, atomic and molecular physics, attosecond science, quantum optics, and will acquire a broad mastery of XUV and charged-particle spectroscopy techniques.
References :
[1] https://www.nobelprize.org/prizes/physics/2023/summary/
[2] Y. Mairesse, et al., Science 302, 1540 (2003)
[3] V. Gruson, et al., Science 354, 734 (2016)
[4] A. Autuori, et al., Science Advances 8, eabl7594 (2022)
[5] C. Bourassin-Bouchet, et al., Phys. Rev. X 10, 031048 (2020)
[6] H. Laurell, et al., Nature Photonics, https://doi.org/10.1038/s41566-024-01607-8 (2025)
Mesure de la réponse intra-pixel de détecteur infrarouge à base de HgCdTe avec des rayons X pour l’astrophysique
In the field of infrared astrophysics, the most commonly used photon sensors are detector arrays based on the HgCdTe absorbing material. The manufacturing of such detectors is a globally recognized expertise of CEA/Leti in Grenoble. As for the Astrophysics Department (DAp) of CEA/IRFU, it holds renowned expertise in the characterization of this type of detector. A key characteristic is the pixel spatial response (PSR), which describes the response of an individual pixel in the array to the point-like generation of carriers within the absorbing material at various locations inside the pixel. Today, this detector characteristic has become a critical parameter for instrument performance. It is particularly crucial in applications such as measuring galaxy distortion or conducting high-precision astrometry. Various methods exist to measure this quantity, including the projection of point light sources and interferometric techniques. These methods, however, are complex to implement, especially at the cryogenic operating temperatures of the detectors.
At the DAp, we propose a new method based on the use of X-ray photons to measure the PSR of infrared detectors. By interacting with the HgCdTe material, the X-ray photon generates carriers locally. These carriers then diffuse before being collected. The goal is to derive the PSR by analyzing the resulting images. We suggest a two-pronged approach that integrates both experimental methods and simulations. Data analysis methods will also be developed. Thus, the ultimate objective of this thesis is to develop a new, robust, elegant, and fast method for measuring the intra-pixel response of infrared detectors for space instrumentation. The student will be based at the DAp. This work also involves collaboration with CEA/Leti, combining the instrumental expertise of the DAp with the technological knowledge of CEA/Leti.
Development and characterization of a reliable 13.5 nm EUV OAM carrying photon beamline
The Extreme UltraViolet (EUV) photon energy range (10-100 nm) is crucial for many applications spanning from fundamental physics (attophysics, femto-magnetism) to applied domains such as lithography and nanometer scale microscopy. However, there are no natural source of light in this energy domain on Earth because photons are strongly absorbed by matter, requiring thus vacuum environment. People instead have to rely on expensive large-scale sources such as synchrotrons, free electron lasers or plasmas from large lasers. High order laser harmonic generation (HHG), discovered 30 years ago and recognized by the Nobel Prize in Physics in 2023, is a promising alternative as a laboratory scale EUV source. Based on a strongly nonlinear interaction between an ultrashort intense laser and an atomic gas, it results in the emission of EUV pulses with femto to attosecond durations, very high coherence properties and relatively large fluxes. Despite intensive research that have provided a clear understanding of the phenomenon, it has up to know been mostly limited to laboratories. Breaching the gap towards applied industry requires increasing the reliability of the beamlines, subjects to large fluctuations due to the strong nonlinearity of the mechanism, and developing tools to measure and control their properties.
CEA/LIDYL and Imagine Optic have recently joined their expertise in a join laboratory to develop a stable EUV beamline dedicated to metrology and EUV sensors. The NanoLite laboratory, hosted at CEA/LIDYL, is based on a high repetition rate compact HHG beamline providing EUV photons around 40eV. Several EUV wavefront sensors have been successfully calibrated in the past few years. However, new needs have emerged recently, resulting in the need to upgrade the beamline.
The first objective of the PhD will be to install a new HHG geometry to the beamline to enhance its overall stability and efficiency and to increase the photon energy to 92eV, a golden target for lithography. He will then implement the generation of a EUV beam carrying orbital angular momentum and will upgrade Imagine Optic’s detector to characterize its OAM content. Finally, assisted by Imagine Optic engineers, he will develop a new functionality to their wavefront sensors in order to enable large beam characterization.
Effect of water radiolysis on the hydrogen absorption flux by austenitic stainless steels in the core of a nuclear pressurized water reactor
In pressurized water nuclear reactors, the core components are exposed to both corrosion in the primary medium, pressurized water at around 150 bar and 300°C, and to neutron flux. The stainless steels in the core are damaged by a combination of neutron bombardment and corrosion. In addition, radiolysis of the water can have an impact on the mechanisms and kinetics of corrosion, the reactivity of the medium and, a priori, the mechanisms and kinetics of hydrogen absorption by these materials. This last point, which has not yet been studied, may prove problematic, as hydrogen in solid solution in steel can lead to changes in (and degradation of) the mechanical properties of the steel and induce premature cracking of the part. This highly experimental thesis will focus on the study of the impact of radiolysis phenomena on the corrosion and hydrogen uptake mechanisms of a 316L stainless steel exposed to the primary medium under irradiation. Hydrogen will be traced by deuterium, and neutron irradiation simulated by electron irradiation on particle accelerators. An existing permeation cell will be modified to allow in operando measurement by mass spectrometry of the deuterium permeation flux through a sample exposed to the simulated primary water under radiolysis conditions. The distribution of hydrogen in the material, as well as the nature of the oxide layers formed, will be analysed in detail using state-of-the-art techniques available at the CEA and in partner laboratories. The doctoral student will ultimately be required to (i) identify the mechanisms involved (corrosion and hydrogen entry), (ii) estimate their kinetics and (iii) model the evolution of hydrogen flux in the steel in connection with radiolysis activity.
Influence of ionization density in water on fluorescent solutes. Application to the detection of alpha radiation
The location and rapid identification, at a distance, of sources of alpha and beta particle emissions on surfaces or in wet cavities or solutions, in nuclear facilities undergoing decommissioning or to be cleaned up, is a real challenge.
The aim of the proposed PhD project is to develop a concept for the remote detection of fluorescence light from water radiolysis processes on molecules or nano-agents. Temporal characterization using fluorescence lifetime measurements will enable detection to be attributed to a type of radiation, depending on its linear energy transfer (LET). In the Bragg peak of alpha radiation, where the TEL is maximal, the ionization density due to this TEL influences the fluorescence lifetime. However, dose rate effects also need to be considered.
Molecules and nanoparticles that are candidates for forming fluorescent products and are sensitive to the ionization density and radicals produced in traces at very short times will be identified by guided bibliography work, then tested and compared by measurements. Spectral measurements (absorption and fluorescence) and fluorescence lifetimes of the corresponding fluorescent species will be carried out using the multi-channel (16-channel) TCSPC (Time Corelated Single Photon Counting) method. Ion beams or alpha particles from sealed sources will be used for proof-of-concept. Ion beams or alpha particles from sealed sources will be used for proof-of-concept in the CEA clean-up/dismantling program.