XUV digital in-line holography using high-order harmonics

A step towards a successful implementation of timeresolved digital in-line holography with extreme ultraviolet radiation is presented. Ultrashort XUV pulses are produced as high-order harmonics of a femtosecond laser and a Schwarzschild objective is used to focus harmonic radiation at 38 nm and to produce a strongly divergent reference beam for holographic recording. Experimental holograms of thin wires are recorded and the objects reconstructed. Descriptions of the simulation and reconstruction theory and algorithms are also given. Spatial resolution of few hundreds of nm is potentially achievable, and micrometer resolution range is demonstrated.Comment: 8 pages, 8 figure

Wavefront performance analysis of Laser MégaJoule optical components

We present a review of recent analysis of optical specifications for the Laser Mégajoule (LMJ) plain size (40 cm × 40 cm) components. Our studies are mainly achieved using the Miró laser propagation code. The purpose of this paper is first to describe the different methods used to model the wavefronts transmitted by the components. Then, we give examples of evaluation results for the following issues: surface imperfection specification on the 1ω phase plate, surface conditioning defects tolerance on 1ω transport mirrors, Power Spectral Distribution (PSD) specifications of the transmitted wavefront and of the roughness on the components of the amplifying section

Propriétés de cohérence spatiale d'un faisceau d'harmoniques

Nous avons étudié les propriétés de cohérence spatiale d'un faisceau harmonique à 55nm dans deux expériences distinctes. D'une part, nous caractérisons la taille et la divergence du faisceau au foyer d'un miroir sphérique. D'autre part, nous mesurons le degré de cohérence spatiale dans le faisceau, par une technique d'interférométrie à division de front d'onde. Les deux mesures caractérisent une bonne cohérence spatiale du faisceau, paramètre M2≈2 et degré de cohérence spatiale γ ≈ 0.5, qui peut être utilisée dans les applications

Source UVX cohérente et ultrabrève par génération d'harmoniques d'un laser intense

La génération d'harmoniques d'ordre élevé dans les gaz est une source de rayonnement UVX aux propriétés uniques notamment de cohérence spatiale et de courte durée. L'étude de la cohérence temporelle de l'émission est intéressante pour les applications, mais également du point de vue fondamental car elle donne des informations sur les mécanismes de la génération. Nous montrons que la phase intrinsèque du dipôle atomique induit un "chirp" de l'émission harmonique plus ou moins important suivant les conditions de génération

Coherence properties of high harmonics and their applications

We recall the main characteristics of high harmonic generation (HHG) by intense laser pulses in gas, which proceed from the fact that HHG is a laser-driven non linear process. We particularly outline the properties of intrinsic, spatial and temporal coherence which are investigated experimentally. We show that they can be controlled through various phase-matching parameters, on account of the particular form of the atomic dipole phase involved in HHG. Finally, we present two feasibility experiments demonstrating that this XUV source can be effectively used in time-resolved interferometry measurements, in particular in the diagnostic of laser-produced ultra-short dense plasmas

Coherence properties of high-order harmonics : Application to high-density laser-plasma diagnostic

We present two interferometry schemes in the extreme ultraviolet, based on either the wave-front division of a unique harmonic beam (1st scheme) or two spatially separated, phase-locked harmonic sources (2nd scheme). In the first scheme using a Fresnel bimirror interferometer, we measure the degree of spatial coherence of the 13 th harmonic generated in xenon, as a function of different parameters. A high degree of coherence, larger than 0.5, is found for the best conditions in almost the full section of the beam. Then, we demonstrate that the second scheme can be used for interferometry measurements with an ultrahigh time resolution. The 11th harmonic is used to study the spatial variation of the electron density of a laser-produced plasma. Electronic densities higher than 2.10 20 cm -3 are measured

A table-top ultrashort light source in the extreme ultraviolet for circular dichroism experiments

Circular dichroism in the extreme ultraviolet range is broadly used as a sensitive structural probe of matter, from the molecular photoionization of chiral species1, 2, 3 to the magnetic properties of solids4. Extending such techniques to the dynamical regime has been a long-standing quest of solid-state physics and physical chemistry, and was only achieved very recently5 thanks to the development of femtosecond circular extreme ultraviolet sources. Only a few large facilities, such as femtosliced synchrotrons6, 7 or free-electron lasers8, are currently able to produce such pulses. Here, we propose a new compact and accessible alternative solution: resonant high-order harmonic generation of an elliptical laser pulse. We show that this process, based on a simple optical set-up, delivers bright, coherent, ultrashort, quasi-circular pulses in the extreme ultraviolet. We use this source to measure photoelectron circular dichroism on chiral molecules, opening the route to table-top time-resolved femtosecond and attosecond chiroptical experiments