Accord de phase et quasi-accord de phase en génération d'harmoniques d'ordres élevés (effet de la pression et du guidage laser)

L'interaction d'une impulsion laser intense (~10 W /cm ) et de courte durée (femtoseconde) avec un gaz rare induit une polarisation hautement non-linéaire dans le domaine spectral XUV; les harmoniques d'ordre élevés. En raison des propriétés spécifiques du rayonnement harmonique et de ses applications, cette thématique est particulièrement riche et fertile. La production efficace d'harmoniques d'ordres élevés repose à la fois sur la réponse non-linéaire de l'atome unique et un comportement collectif.Le fil directeur des études présentées dans cette thèse est la compréhension et le contrôle de l'accord de phase ou du quasi accord de phase en présence d'une ionisation substantielle du gaz générateur. Dans ce contexte, nous montrons l'importance de la longueur de cohérence sur l'accord de phase en génération d'harmoniques. Nous étudions sa dépendance en fonction de la focalisation du laser, de la pression mais aussi sa dépendance temporelle liée à l'ionisation, effet que nous avons mis en évidence lorsqu'on a cherché à optimiser une double impulsion harmonique. Le travail de développement, sur la station LASERIX, de la source à double impulsion harmonique générée à partir d'un même milieu gazeux et avec un délai picoseconde variable est présenté. Cette source possède un véritable potentiel d'applications scientifiques, injectée dans un milieu amplificateur plasma qu'on appelle laser X, la double impulsion permettra de sonder la réponse temporelle de ce type de milieu. Par ailleurs, des expériences et des simulations menées sur la génération d'harmoniques en propagation guidée visent ainsi à étendre les spectres harmoniques vers les courtes longueurs d'ondes, zone spectrale pour laquelle le laser X à plasmas est émis. Ceci donnera l'accès à une source offrant des caractéristiques complémentaires des lasers X, sources développées en parallèle sur la station LASERIX.The interaction of an intense laser pulse of short duration with a rare gas induces a highly non-linear polarization in the XUV spectral range: the high order harmonics. Due to the specific properties of the harmonic radiation and its applications, this issue is particularly rich and fertile. The efficient production of high order harmonics is based both on the non-linear response of the single atom and on collective behavior.The principle of the research presented in this thesis is the understanding and control of phase matching or quasi-phase matching in the presence of substantial ionization in the generating gas. In this context, we show the importance of the coherence length on the phase matching in High harmonic generation. We study its dependence on laser focusing, pressure but also its time dependence related to ionization. Moreover, experiments and simulations aim at extending harmonic spectra towards shorter wavelengths, a spectral range for which the X Ray Laser is emitted. This will give access to a source with complementary characteristics as regards to X-ray lasers. This source shall be developed in parallel on the LASERIX station or injected in soft X-ray laser amplifiers.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Design and characterization of extreme-ultraviolet broadband mirrors for attosecond science

International audienceA novel multilayer mirror was designed and fabricated based on a recently developed three-material technology aimed both at reaching reflectivities of about 20% and at controlling dispersion over a bandwidth covering photon energies between 35 and 50 eV. The spectral phase upon reflection was retrieved by measuring interferences in a two-color ionization process using high-order harmonics produced from a titanium: sapphire laser. We demonstrate the feasibility of designing and characterizing phase-controlled broadband optics in the extreme-ultraviolet domain, which should facilitate the manipulation of attosecond pulses for applications

Extreme-ultraviolet vector-vortex beams from high harmonic generation

[EN]Structured light in the short-wavelength regime opens exciting avenues for the study of ultrafast spin and electronic dynamics. Here, we demonstrate theoretically and experimentally the generation of vector-vortex beams (VVB) in the extreme ultraviolet through high-order harmonic generation (HHG). The up-conversion of VVB, which are spatially tailored in their spin and orbital angular momentum, is ruled by the conservation of the topological Pancharatnam charge in HHG. Despite the complex propagation of the driving beam, high-harmonic VVB are robustly generated with smooth propagation properties. Remarkably, we find out that the conversion efficiency of high-harmonic VVB increases with the driving topological charge. Our work opens the possibility to synthesize attosecond helical structures with spatially varying polarization, a unique tool to probe spatiotemporal dynamics in inhomogeneous media or polarization-dependent systems.European Research Council (851201); Ministerio de Ciencia de Innovación y Universidades, Agencia Estatal de Investigación and European Social Fund (PID2019-106910GB-I00, RYC-2017-22745); Junta de Castilla y León and FEDER Funds (SA287P18); Université Paris-Saclay (2012-0333T-OASIS, 50110000724-OPTX, PhOM REC-2019-074-MAOHAm); Conseil Régional, Île-de-France (501100003990); Barcelona Supercomputing Center (FI-2020-3-0013)

Extreme-ultraviolet structured beams via high harmonic generation

Funding European Research Council (851201); Ministerio de Ciencia de Innovación y Universidades, Agencia Estatal de Investigaci ́on and European Social Fund (PID2019106910GB-I00, RYC-2017-22745); Junta de Castilla y León and FEDER Funds (SA287P18); Université ParisSaclay (2012-0333TOASIS, 50110000724-OPTX, PhOM REC-2019-074-MAOHAm); Conseil Régional, I ˆle-de-France (501100003990); Barcelona Supercomputing Center (FI2020-3-0013).Vigorous efforts to harness the topological properties of light have enabled a multitude of novel applications. Translating the applications of structured light to higher spatial and temporal resolutions mandates their controlled generation, manipulation, and thorough characterization in the short-wavelength regime. Here, we resort to high-order harmonic generation (HHG) in a noble gas to upconvert near-infrared (IR) vector, vortex, and vector-vortex driving beams that are tailored, respectively, in their spin angular momentum (SAM), orbital angular momentum (OAM), and simultaneously in their SAM and OAM. We show that HHG enables the controlled generation of extreme-ultraviolet (EUV) vector beams exhibiting various spatially dependent polarization distributions, or EUV vortex beams with a highly twisted phase. Moreover, we demonstrate the generation of EUV vector-vortex beams (VVB) bearing combined characteristics of vector and vortex beams. We rely on EUV wavefront sensing to unambiguously affirm the topological charge scaling of the HHG beams with the harmonic order. Interestingly, our work shows that HHG allows for a synchronous controlled manipulation of SAM and OAM. These EUV structured beams bring in the promising scenario of their applications at nanometric spatial and sub-femtosecond temporal resolutions using a table-top harmonic source

Extreme-ultraviolet structured beams via high harmonic generation

Funding European Research Council (851201); Ministerio de Ciencia de Innovación y Universidades, Agencia Estatal de Investigaci ́on and European Social Fund (PID2019106910GB-I00, RYC-2017-22745); Junta de Castilla y León and FEDER Funds (SA287P18); Université ParisSaclay (2012-0333TOASIS, 50110000724-OPTX, PhOM REC-2019-074-MAOHAm); Conseil Régional, I ˆle-de-France (501100003990); Barcelona Supercomputing Center (FI2020-3-0013).Vigorous efforts to harness the topological properties of light have enabled a multitude of novel applications. Translating the applications of structured light to higher spatial and temporal resolutions mandates their controlled generation, manipulation, and thorough characterization in the short-wavelength regime. Here, we resort to high-order harmonic generation (HHG) in a noble gas to upconvert near-infrared (IR) vector, vortex, and vector-vortex driving beams that are tailored, respectively, in their spin angular momentum (SAM), orbital angular momentum (OAM), and simultaneously in their SAM and OAM. We show that HHG enables the controlled generation of extreme-ultraviolet (EUV) vector beams exhibiting various spatially dependent polarization distributions, or EUV vortex beams with a highly twisted phase. Moreover, we demonstrate the generation of EUV vector-vortex beams (VVB) bearing combined characteristics of vector and vortex beams. We rely on EUV wavefront sensing to unambiguously affirm the topological charge scaling of the HHG beams with the harmonic order. Interestingly, our work shows that HHG allows for a synchronous controlled manipulation of SAM and OAM. These EUV structured beams bring in the promising scenario of their applications at nanometric spatial and sub-femtosecond temporal resolutions using a table-top harmonic source

Optimisation d'une source d'harmoniques d'ordres élevés pour l'optique non-linéaire dans l'extrême UV

The work presents the development of the high harmonic source at LOA, based on a kHz Titanium-Sapphire laser system. Our aim is to provide a source optimized for the study of interactions between an intense high harmonic beam, focused onto a solid target. The framework of this optimization is set, both theoretically and experimentally, that led to absorption-limited generation conditions. We particularly emphasize the importance of aperturing the infrared laser beam. We demonstrate the application of an efficient genetic algorithm to the spectral control of the harmonic radiation through the control of the infrared laser spectral phase. We conclude on the focusing of harmonic beams.Cette thèse présente le travail réalisé sur la source harmoniques du LOA à partir d'une chaine Titane-Saphir kHz. Cette étude s'inscrit dans la perspective d'observer des effets non linéaires dus à l'interaction d'un faisceau harmonique intense focalisé sur cible solide. Nous présentons l'étude de l'optimisation de cette source, qui permet de générer efficacement des harmoniques en limite d'absorption. Un cadre complet d'étude de ces conditions d'optimisation du point de vue théorique et expérimental est défini avec notamment une explication détaillée de l'importance de la diaphragmation du faisceau infrarouge. Nous montrons également comment la technique des algorithmes génétiques a été utilisé par le controle de la phase spectrale du laser de pompe. Nous concluons sur la focalisation des harmoniques

Compression of attosecond harmonic pulses by extreme-ultraviolet chirped mirrors

International audienceIn the race toward attosecond pulses, for which high-order harmonics generated in rare gases are the best candidates, both the harmonic spectral range and the spectral phase have to be controlled. We demonstrate that multilayer extreme-ultraviolet chirped mirrors can be numerically optimized and designed to compensate for the intrinsic harmonic chirp that was recently discovered and that is responsible for temporal broadening of pulses. A simulation shows that an optimized mirror is capable of compressing the duration from 260 to 90 as. This new technique is an interesting solution because of its ability to cover a wider spectral range than other technical devices that have already been proposed to overcome the chirp of high harmonics

Compression of attosecond harmonic pulses by extreme-ultraviolet chirped mirrors

International audienceIn the race toward attosecond pulses, for which high-order harmonics generated in rare gases are the best candidates, both the harmonic spectral range and the spectral phase have to be controlled. We demonstrate that multilayer extreme-ultraviolet chirped mirrors can be numerically optimized and designed to compensate for the intrinsic harmonic chirp that was recently discovered and that is responsible for temporal broadening of pulses. A simulation shows that an optimized mirror is capable of compressing the duration from 260 to 90 as. This new technique is an interesting solution because of its ability to cover a wider spectral range than other technical devices that have already been proposed to overcome the chirp of high harmonics

Shack-Hartmann Wavefront Sensing of Ultrashort Optical Vortices

Light beams carrying Orbital Angular Momentum (OAM), also known as optical vortices (OV), have led to fascinating new developments in fields ranging from quantum communication to novel light–matter interaction aspects. Even though several techniques have emerged to synthesize these structured-beams, their detection, in particular, single-shot amplitude, wavefront, and modal content characterization, remains a challenging task. Here, we report the single-shot amplitude, wavefront, and modal content characterization of ultrashort OV using a Shack-Hartmann wavefront sensor. These vortex beams are obtained using spiral phase plates (SPPs) that are frequently used for high-intensity applications. The reconstructed wavefronts display a helical structure compatible with the topological charge induced by the SPPs. We affirm the accuracy of the optical field reconstruction by the wavefront sensor through an excellent agreement between the numerically backpropagated and experimentally obtained intensity distribution at the waist. Consequently, through Laguerre–Gauss (LG) decomposition of the reconstructed fields, we reveal the radial and azimuthal mode composition of vortex beams under different conditions. The potential of our method is further illustrated by characterizing asymmetric Gaussian vortices carrying fractional average OAM, and a realtime topological charge measurement at a 10Hz repetition rate. These results can promote Shack-Hartmann wavefront sensing as a single-shot OV characterization tool

Optimisation de la génération d'harmoniques d'ordre élevé à l'aide d'une optique adaptative et d'un modulateur acousto-optique

International audienceAfin de contrôler la génération d'harmoniques d'ordre élevé dans des conditions optimisées, nous avons réalisé des expériences préliminaires de contrôle spectral et spatial du laser infrarouge. Nous avons démontré la possibilité de modifier la longueur d'onde des harmoniques grâce à la modification de la phase spectrale du laser infrarouge par un modulateur acousto-optique « Dazzler ». Nous montrons que cette méthode permet d'obtenir un spectre plus large et un flux de photon intégré beaucoup plus important qu'en utilisant une simple modification de la dérive de fréquence du laser. Nous présentons également les premiers résultats de mise en forme de la tache focale du laser par optique adaptative, et l'effet de ce contrôle spatial sur la génération d‘harmoniques