Thèse Contrôle et Manipulation d'Un Faisceau Laser Euv H/F - Doctorat.Gouv.Fr

Établissement : Université Paris-Saclay GS Physique École doctorale : Ondes et Matière Laboratoire de recherche : CEA/LIDYL - Laboratoire Interactions, Dynamique et Lasers Direction de la thèse : Willem BOUTU ORCID 0000000311375724 Début de la thèse : 2026-10-01 Date limite de candidature : 2026-06-30T23:59:59 Le domaine spectral de l'ultraviolet extrême (EUV, entre 10 et 100 nm) est crucial pour de nombreuses applications, de la physique fondamentale à des domaines plus appliqués. Cependant, il n'y a pas de source naturelle de lumière EUV sur Terre car ces photons sont absorbés par la matière. Les chercheurs doivent utiliser des installations complexes, de grandes tailles et chères telles que les synchrotrons et les lasers à électrons libres. La génération d'harmoniques laser d'ordre élevé, découverte il y a 30 ans et récompensée par le Prix Nobel de Physique en 2023, est une alternative prometteuse à l'échelle d'un laboratoire. Issue de l'interaction hautement non linéaire entre une impulsion laser intense ultrabrève et un gaz atomique, elle résulte en l'émission d'impulsions EUV de durées ultracourtes, avec une très grande cohérence spatiale et des flux importants. Cependant, ces développements ont jusqu'à présent principalement été limités aux laboratoires de recherche. Combler le fossé avec l'industrie impose d'améliorer la fiabilité de ces lignes de lumière et de développer des outils nouveaux pour mesurer et contrôler leurs propriétés, tous deux objectifs de cette thèse. The Extreme UltraViolet (XUV) 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 XUV source [1]. Based on a strongly nonlinear interaction between an ultrashort intense laser and an atomic gas, it results in the emission of XUV 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. Bridging 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 is a research laboratory dedicated to the study of laser-matter ultrafast interaction, with a major expertise in the study, development and use of XUV beamlines from HHG in gases, crystals and plasmas. Imagine Optic is a SME that designs, develops, manufactures and commercializes wavefront metrology and adaptive optics from the IR to the X-ray domains. CEA/LIDYL and Imagine Optic have recently joined their expertise in a join laboratory to develop a stable XUV beamline dedicated to metrology and XUV sensors [2] Objective 1: Upgrade of the XUV metrology beamline
Metrology and calibration of XUV detectors require a very stable photon source in terms of flux, pointing and spatial profile. This is usually achieved by either letting the beam propagating over a very long distance, in effect filtering out its central part at the expense of the size of the setup because of the very low divergence of XUV radiations, and of the photon flux. Another technique consists in focusing the XUV radiation in a small filtering pinhole, here also at the expense of the flux.
More than ten years ago researchers tried another route to control the XUV phase front quality by inserting adaptative optics on the generating laser. However, because of the inherent instabilities of the Ti:Sa high energy lasers used at that time, these studies were mostly inconclusive. Indeed, because of the very high nonlinearity of the XUV generation process, any fluctuation in the IR beam properties is highly amplified in the XUV. We propose in this PhD project to push active XUV phase control, taking advantage of the new Yb-doped fiber laser available at the NanoLight platform. Its shot-to-shot and long-term stabilities, together with its almost perfect phase profile, will insure reproducibility in the XUV generation conditions. The deformable mirror will be coupled with a XUV wavefront sensor to monitor the XUV quality in real time and with another one installed on the IR beam to study the coupling between the IR and XUV profiles.
In addition, we will install a new XUV focusing optic to reach (sub)micrometer scale focusing. The real time characterization of the XUV wavefront will be coupled with the deformable mirror and remote alignment of the mirror to enable reaching a high quality highly divergent beam without compromising on the photon flux.
In parallel, there is a strong incentive to decrease the wavelength range of the beamline. Indeed, providing photons around 12-14 nm would enable the calibration of soft X-ray wavefront sensors without the need for expensive and hard to get synchrotron beamtimes. Moreover, 13.5 nm is one of the key wavelengths for lithography. Gaining access to this specific range would open up the possibilities for the join laboratory. Increasing the photon energy range for the beamline can be achieved by changing the nonlinear medium, at the expense however of a drastic loss of photon flux. Instead, the student will implement a laser postcompression stage, which consists in reducing the pulse duration of the driving laser, thus increasing the laser intensity while reducing detrimental ionization effects. CEA/LIDYL laser group has a strong expertise in laser postcompression and will provide technical and numerical supports to the student [3].
Objective 2: Upgrading and testing the wavefront sensor for OAM characterization
Light can carry two angular momenta. The first one, the spin angular momentum, corresponds to light polarization. The second one, the orbital angular momentum (OAM), is experiencing a strong rise of interest in the XUV community with applications in chirality, spintronics, opto-electronics or orbitronics to name a few. This additional degree of freedom opens up new control routes with huge potential impacts to increase the speed and lowering the energy consumption of future electronics components. However, OAM is difficult to impart to XUV pulses, and most solutions result in non-perfect OAM modes [4,5]. Moreover, because of the limited energy per pulse available at NanoLight, standard techniques using either an OAM carrying IR beam (resulting in very large OAM numbers in the XUV) or multi-beam alternatives will not be possible. We propose to implement OAM control on the HHG beamline using specifics XUV transmission optics designed by our collaborators from IST Lisbon and MQP Paris Cité. The beamline will then be used to transfer the technology developed by Imagine Optic to characterize OAM from the visible range to the XUV.
Objective 3: Development of large numerical aperture measurement by wavefront stitching
Past experiences in the join laboratory have shown that measurements are often limited by the detector numerical aperture, which is usually smaller than the source divergence. Imagine Optic has started to develop a solution based on the stitching of multiple overlapping acquisitions spanning the whole sensor aperture. The student will work with their software engineers to consolidate their algorithm needed to calibrate high NA wavefront sensors. A first demonstration on NanoLite beamline will consist in characterizing the quality of the focusing of the XUV beam by the newly implemented focusing optics (Obj. 1). This will help to improve the alignment of this optic and enhance the beam's spatial properties [6].

Master 2 physique avec des bases en optique et laser.