Étude de la génération d'harmoniques anormales d'ordre élevé à basse intensité

Nous présentons des résultats expérimentaux de spectre d'harmoniques anormales d'ordre élevé générées à basse intensité laser (2 10$^{13}$ W$\!/$cm$^2$) dans l'argon. Ce spectre ne peut pas être expliqué par le modèle classique à trois étapes qui prédit les caractéristique du spectre . Les ordres observés dans notre mesure vont bien au delà de la limite de la coupure donnée par l'intensité du laser dans le milieu gazeux. De plus, nous n'observons pas les ordres très bas. Nous présentons une étude systématique de ces spectres, ainsi que des simulations numériques issues de la résolution de l'équation de Schrödinger dépendante du temps

Optimization of the focused flux of high harmonics

Following the theoretical predictions [1], the observation of two-photon processes by interaction of vacuum ultraviolet (VUV) radiation with inner-shell levels of atoms requires focused intensities in the $10^{13}{-}10^{14}$ W/cm2 range. Our aim is to reach this regime in order to study non-linear optics at these wavelengths. We first optimized the high harmonic conversion efficiency in argon by studying the best experimental conditions for phase-matching, concentrating on focus geometry related to laser energy, cell length and position relative to the focus. We then studied the resulting harmonic beam focusability by a toroidal mirror (f=10 cm) and made an image of the harmonic focus. We conclude with an evaluation of the focused intensity that we are able to reach experimentally

SIRIUS is a state-of-the-art detector system for nuclear decay spectroscopy that will be mounted at the focalplane of S3 (Super Separator Spectrometer), which is part of the new SPIRAL2 facility at GANIL, Caen in France. Such a systemrequires high performance as it is dedicated to the study of very exotic nuclei. It is the result of collaboration between GANILCSNSM, IRFU, and IPHC It is composed of a succession of detectors (Trackers, Silicon detector DSSD and Tunnel plus anarray of five clover Germanium detectors). This set-up is mounted in a compact geometry. The energy measurement variesfrom 50 keV to over 500 MeV with high precision (2 x 10-3) at low energies and 1 % for the detection of heavy ions. A majorchallenge has been the development of new electronics with a very large dynamic range maintaining an adequate energyresolution for the measured particles (with energies from a few hundred keV up to 500 MeV).

International audienceSIRIUS is a state-of-the-art detector system for nuclear decay spectroscopy that will be mounted at the focal plane of S$^3$ (Super Separator Spectrometer), which is part of the new SPIRAL2 facility at GANIL, Caen in France. Such a systemrequires high performance as it is dedicated to the study of very exotic nuclei. It is the result of collaboration between GANILCSNSM, IRFU, and IPHC It is composed of a succession of detectors (Trackers, Silicon detector DSSD and Tunnel plus anarray of five clover Germanium detectors). This set-up is mounted in a compact geometry. The energy measurement variesfrom 50 keV to over 500 MeV with high precision (2 x 10$^{-3}$) at low energies and 1 % for the detection of heavy ions. A majorchallenge has been the development of new electronics with a very large dynamic range maintaining an adequate energyresolution for the measured particles (with energies from a few hundred keV up to 500 MeV)