Thèse Étude des Optiques à Gradient d'Indice Complexes et Structurées par Laser H/F - 75

Établissement : Université Paris-Saclay GS Physique
École doctorale : Ondes et Matière
Laboratoire de recherche : ONERA/DOTA - Département Optique et Techniques Associées
Direction de la thèse : Guillaume DRUART ORCID 0009000139820204
Début de la thèse : 2026-10-01
Date limite de candidature : 2026-04-30T23:59:59

L'objectif de la thèse est d'étudier le potentiel des optiques GRIN complexes (CGRIN) pouvant être obtenues en structurant la matière à l'aide d'un laser femtoseconde afin de répondre aux problématiques SWAP. Ce travail exigera que le doctorant relève les défis liés à la conception, à la fabrication et à la métrologie des optiques CGRIN.

The field of imaging has undergone a revolution, initially in the visible spectrum, thanks to the reduction in pixel size, which has made it possible to effectively address the SWAP-C (size, weight, power, and cost) issue. This revolution has led to the widespread use of imaging in society with the emergence of new applications. The field of infrared imaging is also following this same trend. The main challenge now lies in the optical component, which is governed by its first-order characteristics (focal length, aperture) and by the physics of diffraction, which limits the optical resolution of the system. With smaller pixels, the optics must be more open in order to reduce the diffraction spot. This significant constraint means that simply adapting an old optical system is not possible, and new strategies must be devised to continue to address the SWAP-C issue. An initial strategy consisted of making optical surfaces more complex (aspherical, freeform) in order to increase the number of degrees of freedom without increasing the number of surfaces in the optical system. The second strategy consists of drawing inspiration from nature by using gradient index optics (known as GRIN lenses), i.e., optics whose index varies across their volume. As GRINs are more complex to produce than surface etching and polishing, the GRIN solution has so far been neglected in favor of complex surfaces. The recent emergence of new technologies for manufacturing GRIN optics (3D printing, laser structuring, stacking of polymer nanolayers, etc.) has brought GRIN optics back to the forefront. These technologies make it possible to consider complex GRINs (freeform, discontinuous, etc.). Furthermore, the combination of complex surfaces with complex GRINs (CGRINs) is entirely feasible for creating very open SWAP systems that are compatible with very small pixels. However, as with any emerging field, there are many challenges to be overcome, such as the optimization of systems with multiple degrees of freedom, their manufacture, and their metrology.
A Dutch thesis published in 2025 discusses the value of GRINs for SWAP-C issues. Several Dutch universities are participating in the FOCUS (Future Optical Components for Ultimate Dispersion Control Strategies) program, which focuses on freeform GRINs (FGRINs) obtained by 3D printing from nanoparticles-doped polymers (concept developed by American startup Nanovox following a DARPA project). The program plans to launch 12 theses in the field of FGRIN starting in 2026. These theses will address issues of design, materials, manufacturing, and metrology.

Implementation of an index gradient model obtained by femtosecond laser in optical design codes.
Evaluation of the s-SNOM/nano-FTIR experimental method to control the quality of laser structuring and validate material structuring processes.
Manufacture of complex GRIN obtained by laser structuring

Année 1 : étude bibliographique, prise en main du sujet en s'appuyant sur les thèses de Pierre Delullier et de Paul Mathieu, mesure de la constringence par ellipsométrie d'un GRIN obtenu par structuration laser, implémentation d'un modèle GRIN dans ZEMAX et conception et réalisation d'un système optique. Réalisation d'abaques pour une structuration laser avec un faisceau laser de Bessel.
Année 2 : conception et réalisation par structuration laser de lentilles diffractives multi-niveaux (MDL). Etude de la structuration multi-couches, étude de l'évolution des abaques en fonction de la profondeur de structuration. Conception optique de FGRIN, implémentation d'une bibliothèque CGRIN dans le code FORMIDABLE et évaluation de l'apport de la différentiation dans l'optimisation de CGRIN
Année 3 : Conception et réalisation d'un démonstrateur utilisant un CGRIN. Caractérisation de ce démonstrateur. Rédaction de thèse.