Description du sujet de thèse

This PhD project focuses on the development of broadband, low temporal coherence fiber laser sources designed for next-generation inertial confinement fusion (ICF) laser systems. The work will be carried out at the Laboratoire pour l'Utilisation des Lasers Intenses (LULI), located at École polytechnique (CNRS, Palaiseau), in collaboration with the Centre Lasers Intenses et Applications (CELIA) at the University of Bordeaux (Talence).

In 2022, the National Ignition Facility (NIF) in the United States achieved the first-ever net energy gain from an ICF experiment, marking a pivotal breakthrough in fusion research. Since then, several international efforts have emerged to develop low-carbon power plants based on ultra-intense lasers. In France, the Taranis project—selected in March 2024 as part of the France 2030 initiative—is a key example of this effort. Led by the startup GenF (a Thales spin-off), the project brings together a national consortium including Thales, CEA, CNRS, LULI, and CELIA.

Within this context, LULI is responsible for several work packages, notably the development of novel laser sources to test advanced ICF concepts, particularly in direct-drive configurations. Unlike traditional systems based on highly coherent lasers, this thesis investigates the use of broadband, temporally incoherent sources generated through semiconductor optical amplifiers (SOAs). The goal is to improve energy coupling between the laser pulse and the fusion target while reducing undesirable effects such as laser imprinting and parametric instabilities (e.g., Brillouin and Raman backscattering).

The project aims to develop a complete, agile laser source featuring arbitrary shaping capabilities in amplitude, spectrum, and phase, with the objective of integrating it into existing high-power systems such as LULI2000 and Apollon for experimental campaigns in plasma physics.
LULI has established expertise in arbitrary seeding for high-power laser chains and has recently developed technology based on SOAs capable of generating broadband (70 nm) temporally shaped nanosecond incoherent pulses.

The thesis will include both experimental and theoretical/modeling components:
• Theoretical Modeling
• Study of SOA behavior under coherent and incoherent regimes.
• Statistical modeling of intensity spikes and spatio-temporal coupling in incoherent beams.
• Simulations using Python or MATLAB to predict intensity distributions and dynamics relevant to high-power laser chains.
• Experimental Development
• Construction of a broadband fiber laser source based on superluminescent diodes (SLEDs) combined with temporal shaping modules (SOAs) and spectral shaping (waveshapers).
• Amplification using doped fiber amplifiers to reach energy levels suitable for injection into fusion-relevant laser drivers.

Close collaborations are planned with the Taranis consortium, notably with CELIA for testing, validation and possible integration of diagnostics specific to incoherent beams, and with Thales for industrial site experiments. Experimental campaigns are already scheduled on the LULI2000 and Apollon facilities, in partnership with the international plasma physics community.

Candidate profile :
• Education : Master's degree or engineering diploma in laser physics, optics, plasma physics, photonics, or related fields.
• Technical Skills
-Knowledge in high-intensity laser systems and/or fiber laser sources
-Proficiency in scientific programming (Python, MATLAB, C/C++)
-Skills in data analysis, physical modeling, and experimental physics
• Personal Qualities :
-Scientific rigor
-Autonomy
-Strong teamwork
-Communication abilities
-Gor command of Englis is highly desirable

Interested candidates should send: detailed CV, cover letter and scientific references.

Contexte de travail

The Centre National de la Recherche Scientifique (CNRS) is one of the world's leading insti-tutions for fundamental research. LULI is a reference laboratory in high-intensity laser physics and operates on three sites: École polytechnique (Palaiseau), CEA (Orme des Me-risiers), and Sorbonne University (Jussieu). The lab hosts around 110 staff members and operates several large-scale facilities: LULI2000, Apollon, HERA, and XCAN.

The PhD student will join the R&D laser team at LULI and work in close collaboration with members of the Taranis consortium. Visits to partner institutions (Thales, CELIA) are ex-pected, along with participation in major experimental campaigns. A teaching assignment (monitoring/tutoring) can also be considered based on the candidate's interest.

The position is in a sector subject to scientific and technical potential protection (PPST) and, in accordance with regulations, your arrival must therefore be authorised by the competent authority.

Contraintes et risques

Travel within France and internationally is to be expected as part of the mission.