Evidence of resonant surface wave excitation in the relativistic regime through measurements of proton acceleration from grating targets

The interaction of laser pulses with thin grating targets, having a periodic groove at the irradiated surface, has been experimentally investigated. Ultrahigh contrast ($\sim 10^{12}$) pulses allowed to demonstrate an enhanced laser-target coupling for the first time in the relativistic regime of ultra-high intensity >10^{19} \mbox{W/cm}^{2}. A maximum increase by a factor of 2.5 of the cut-off energy of protons produced by Target Normal Sheath Acceleration has been observed with respect to plane targets, around the incidence angle expected for resonant excitation of surface waves. A significant enhancement is also observed for small angles of incidence, out of resonance.Comment: 5 pages, 5 figures, 2nd version implements final correction

High-energy isolated attosecond pulses generated by above-saturation few-cycle fields

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Status of the SPARC-X Project

SPARC-X is a two branch project consisting in the SPARC test facility dedicated to the development and test of critical subsystems such as high brightness photoinjector and a modular expandable undulator for SASE-FEL experiments at 500 nm with seeding, and the SPARX facility aiming at generation of high brilliance coherent radiation in the 1.5-13 nm range, based on the achieved expertise. The projects are supported by MIUR (Research Department of Italian Government) and Regione Lazio. SPARC has completed the commissioning phase of the photoinjector in November 2006. The achieved experimental results are here summarized together with the status of the second phase commissioning plans. The SPARX project is based on the generation of ultra high peak brightness electron beams at the energy of 1 and 2 GeV generating radiation in the 1.5-13 nm range. The construction is at the moment planned in two steps starting with a 1 GeV Linac. The project layout including both RF-compression and magnetic chicane techniques has been studied

Impulsions attosecondes

Des expériences récentes ont démontré que les harmoniques d'ordres élevés sont émises sous la forme d'un train d'impulsion attosecondes [1]. Cette découverte ouvre une nouvelle ère en métrologie puisque les échelles de temps sub-femtosecondes auxquelles évoluent les électrons dans les atomes sont désormais accessibles. Cependant, les techniques de type pompelsonde requièrent la sélection préalable d'une seule impulsion attoseconde. Dans cet article, nous présentons et testons une méthode expérimentale permettant de confiner l'émission harmonique en une seule impulsion attoseconde. Nous présentons ensuite quelques techniques de mesure d'impulsions XUV ultra-courtes puis nous suggérons des applications pour la mesure de processus ultra-rapides

Confinement temporel de la génération d'harmoniques d'ordre élevé

On utilise l'extrême sensibilité des harmoniques à l'ellipticité du champ laser fondamental pour confiner temporellement l'émission harmonique. Nous utilisons une technique linéaire permettant de moduler l'état de polarisation du champ laser infra-rouge de durée $\tau = 35$ fs. On créé ainsi dans l'impulsion laser une porte temporelle où la polarisation est linéaire, et est elliptique en dehors. La porte temporelle de polarisation linéaire est ajustable continûment d'une valeur minimum de 7 fs à l'infini. On génère l'émission harmonique avec cette impulsion laser modulée en polarisation pour observer l'évolution du spectre harmonique en fonction de la durée de la porte temporelle. Les spectres observées expérimentalement sont en bon accord avec un confinement temporelle en deçà de 7 fs. Avec un champ laser fondamental plus court, on devrait être capable d'isoler une seule impulsion attoseconde

Investigation of amplitude spatio-temporal couplings at the focus of a 100 TW-25 fs laser

International audienceWe address the on target focal spot spatio-temporal features of an ultrashort, 100 TW class laser chain by using spectrally resolved imaging diagnostics. The observed spatio-spectral images, which we call rotating imaging spectrographs, are obtained single shot to reveal the essential information about the spatio-temporal couplings. We observe nontrivial effects in the focal plane due to compressor defects which significantly affect the maximum on target intensity. This diagnostic might become an essential tool for improving compressor alignment in many upcoming multi-petawatt short pulse laser facilities

Generation of attosecond pulses with ellipticity-modulated fundamental

We have studied experimentally and theoretically high-order harmonic generation using a laser field with a time-dependent ellipticity. We show that the harmonic emission can be confined into a narrow temporal window, in which the fundamental polarization is quasi-linear. This allows a single attosecond pulse (200 as) with a fundamental field obtained from 10 fs pulse to be generated

Attosecond pulses generation with an ellipticity-modulated laser pulse

Attosecond pulse emission using a laser field with time-dependent ellipticity is studied experimentally and theoretically. Our theoretical approach is validated by comparison with experimental VUV spectra. We show in calculations that the VUV emission can be confined into a narrow temporal window in which the fundamental polarization is quasi-linear. We find an analytical equation describing the duration of this window and compare it with numerical results. The requirements for the fundamental field that are necessary to confine this emission to a single attosecond pulse generation are formulated

Time-resolved measurements of high order harmonics confined by polarization gating

We investigate the temporal confinement of high order harmonic pulses generated by a femtosecond (fs) infrared (IR) pulse with a time varying polarization. We use a set of two birefringent quartz plates to modulate the IR polarization. It produces a short temporal gate of linear polarization where harmonics are efficiently generated during a small fraction of the IR pulse. By rotating one of the plates, the gate width can be continuously varied between 70 fs down to 7 fs. The XUV pulse duration is measured by cross-correlation with a probe IR pulse of 12 fs. When the gate width is decreased, a clear temporal confinement of the XUV emission is observed through the cross correlation signal. This experiment is the first direct experimental evidence in the temporal domain that the polarization gating technique can be used to significantly shorten the harmonic pulse duration