With the advent of PetaWatt (PW) class lasers capable of achieving light intensities I=10^22W.cm-2 at which matter becomes plasma, Ultra-High Intensity (UHI) physics now aims at solving two major challenges: can we reach extreme light intensities approaching the Schwinger limit I=10^29W.cm-2, around which light self-focuses and produces electron-positron pairs in vacuum? Can we achieve high-charge compact particle accelerators with high-beam quality that will be essential to push forward the horizons of high energy science? Solving these major questions with the current generation of high-power lasers will require conceptual breakthroughs that I intend to develop in this project. In particular, I aim to show that so-called ‘relativistic plasma mirrors’, produced when a high-power laser hits a solid target, can provide simple and elegant paths to solve these two challenges. Upon reflection on a plasma mirror surface, lasers can produce high-charge relativistic electron bunches and bright short-wavelength attosecond harmonic beams. Could we use plasma mirrors to tightly focus harmonic beams and reach extreme light intensities, potentially approaching the Schwinger limit? Could we employ plasma mirrors as high-charge electron injectors in a PW laser field of 100TV.m-1, or in a laser wakefield accelerator, to build ultra-compact particle accelerators? In the PLASM-ON-CHIP project, I propose to answer these interrogations ‘on-chip’ using massively parallel simulations on the largest supercomputers, to help devise/validate novel and readily-applicable experimental solutions based on plasma mirrors. To this end, I will make use of our recent transformative developments in ‘first principles’ simulation of UHI laser-plasma interactions that enable the 3D modeling of plasma mirror sources with high-fidelity on current petascale and future exascale supercomputers.

The goal of the project is to develop techniques, in a staged approach, and push for optimization of a compact and high-brightness source of pulsed neutrons, using high-power lasers as a driver. In short, such lasers offer prospect for relatively inexpensive, extremely compact, collimated and fast (MeV) neutron sources, with the advantage of short duration, as demonstrated by our group in 2015 using our patented original concept. This would allow to satisfy the increasing demand for neutron sources, which will be difficult to meet with conventional facilities (accelerators) due to their associated cost (Billions of €). It will also enable a flexible experimental platform to uniquely study neutron interactions in the plasma state (for e.g. the nucleosynthesis of heavy elements in plasmas), which is not possible at conventional facilities where additional particle beams and energy sources to drive high-energy-density plasmas are usually missing. Establishing high-intensity, PetaWatt-class lasers as an attractive alternate for high-flux neutrons sources with relatively lower costs is timely. High-power laser facilities are indeed on a fast rise, and prove to be a very versatile tool to generate a wide range of secondary sources that can be used for scientific or societal applications, but none is yet geared to generate neutrons as a probing secondary source. This project is geared for the new, multi-PetaWatt (PW) Apollon laser users’ facility (financed in the frame of the large “Equipex/Investments for the Future programme” projects). It will associate four French laboratories, in partnership with IFIN-HH/ELI-NP (Romania), who have complementary expertise in laser-driven ion beams and nuclear physics. The project is expected to complement the capabilities of current neutron facilities to expand the field of neutron physics and applications (e.g. neutron radiography and spectroscopy). It will as well widen the applicability of laser-driven ion beam sources, all of which will benefit next-generation large-scale and high repetition rate (up to 10 Hz) facilities presently built in France, the EU and Asia.

Quantum Electrodynamics (QED) is the theory that unifies electromagnetism and quantum mechanics to describe how light and charged particles interact. Considered as one of the most accurately tested theories, it led Richard Feynman to call it “the jewel of physics”. Yet, in its strong-field (SF) regime, when the light fields E are ultra-intense and close to the so-called Schwinger limit (ES>10^18V/m) in the charged particles rest frame, QED has so far remained ‘terra incognita’ in experiments and the developed SF-QED theory has never received an accurate experimental validation. When the electric field is well above the Schwinger limit (E>1600 ES) in the particles rest frame, QED enters the so-called ‘fully non-perturbative regime’ (NP), for which there is currently no accepted theory to describe how light interact with charged particles. Due to the extreme fields values required, the SF and NP regimes of QED are out of the reach of all experiments envisaged so far with current high-power laser technology, that currently offers the most intense source of electric field on earth. To break this barrier, we propose a new approach based on so-called Doppler-boosted lasers, than rely on plasma optical devices dubbed 'plasma mirrors' to considerably boost the intensity of current lasers by orders of magnitude. By colliding such Doppler-boosted lasers with relativistic electron beams produced by laser-plasma accelerators, it could in principle be possible to reach the fully NP regime of QED. The implementation of such experiment is very ambitious, requires many complementary expertise (strong-field quantum electrodynamics, Doppler-boosting with plasma mirrors, high-intensity laser-matter modelling, laser-plasma acceleration and electron beam manipulation, laser and electron beam spatio-temporal characterization) and considerable funding. In this context, we plan to apply for an ERC synergy grant for the upcoming call. We recently set-up an international consortium of three principal investigators and are in the phase of writing the proposal. The present ANR project would help us support our consortium (on-site meetings and brainstorming) as well as finalizing the writing of our proposal (external ERC expert consultant).

The synthesis of crystalline oxide nanoparticles by co-precipitation of ions in water and at room temperature is an industrially appealing method to produce functional nanomaterials: it is suitable for up-scaling; it shows reduced environmental and energetic impact; its generic character allows transposition to virtually any transition metal oxide nanoparticles, offering a broad catalogue of properties for applications. Yet, the development of functional materials from nanoparticles requires an optimal control over their crystallinity (quality and polymorph selection) and nanostructure (size, aggregation state). In the case of crystalline oxide nanoparticles synthesized at room temperature in water, a crucial bottleneck which hampers this control is the failure of the classical models to describe the multi-step process of nucleation at work in such “soft chemistry” syntheses. The new insight brought by the DIAMONS project is to investigate the successive transient states from the solution to the nanocrystals, to understand how they template the crystalline oxide nanoparticles, and how they select the nanoparticle structure/polymorph (Figure 1). These transient states are (i) dense liquid phases that form even before any chemical reaction has occurred, or (ii) a possible succession of amorphous states that develop prior to crystallisation. As both kinds of transient states are presumably ubiquitous in syntheses of oxide nanoparticles in water, their identification is critical in order to reach an optimal control of nanostructure and crystalline lattice, beyond the rule-of-thumb provided by the classical nucleation theory. The implications of the multi-step nucleation are to date poorly explored, not only because of the novelty of the concept, but also because of the great experimental challenge to overcome: the characterisation of transient states from the Angstrom to the submicron scale, at reaction times shorter than one millisecond. We will face the challenge using as model cases the synthesis in water of luminescent rare earth-doped vanadates nanoparticles, namely YVO4:Eu and LaVO4:Eu. In these systems, the control of nanostructure and/or polymorph drastically condition their emission properties, hence their potential as luminescent biolabels or precursor for thin-film phosphors. We will monitor the transient states for reaction times starting from about hundred microseconds using novel microfluidic developments will be coupled with (i) standard laboratory/synchrotron-based X-ray structural characterisations (SAXS, WAXS, EXAFS), (ii) time-resolved luminescence spectroscopy to probe local dynamics and chemical environment, and (iii) total scattering measurements with pair distribution function analysis (PDF) which provides a full description of the local order in disordered media. These experimental observations will constitute input for theoretical modelling based on cutting-edge developments in phase field theory and statistical physics. Such combination of theory and time-resolved, in situ structural and dynamic characterisations will provide generic rules for the control of the morphology and polymorph selection of oxide nanoparticles relevant for their production at industrial level.

Ultrashort laser high order harmonic generation (HHG) in gases have started 30 years ago a new era of real time observation of electron ultrafast dynamics. However, because of the very high electric fields needed to tunnel ionize the atoms, HHG implies the use of amplified and complex laser systems, thus limiting its spreading to state of the art laboratories. However, a recent breakthrough demonstrated that harmonic emission from a simple laser oscillator was possible thanks to the use of plasmonic effects. Moreover, VUV emission from semiconducting crystals was observed a few years ago, opening the way to solid state attosecond sources. The PACHA project aims at explaining the electronic mechanisms at play during those two phenomena. In a first step, we will shed light on the electron dynamics during high order harmonic emission in crystals, dynamics that are not yet well understood. A comprehensive study of harmonic radiation property variations with the crystal nature and the incident laser characteristics will help refine the theoretical models, currently somehow contradictory. By adding nanometric resonant structures to the crystals, electric field amplification effects will enable HHG using fibre lasers that deliver mid infrared low energy pulses. Indeed, longer wavelengths mean higher damage thresholds, and the high repetition rates of those sources lead to shorter integration times. Numerical simulation will be used to optimize the periodic structures. The sample manufacturing will be performed by the project team. The complete harmonic emission spectral characterization, both in amplitude and phase, will give access to electron trajectories and plasmon dynamics. Additionally, the crystal electronic band structure can thus be imagined. Several numerical codes will be developed to analyse the experimental results and propose physical interpretations to the measurements.