For most applications of laser driven ion beams, a well-characterized high repetition rate intense ion beam with low divergence and a controllable energy spectrum is needed. High power laser-solid targets interactions are usually used, in which the main acceleration mechanism is the so-called Target Normal Sheath Acceleration (TNSA). Changing solid targets for overcritical gas jet targets has given interesting results in theoretical simulations and these later have several technical advantages for high repetition rate lasers. In this work protons and helium ions are accelerated from a near-critical supersonic gas jet. The production of such targets is very challenging for near infrared lasers. We present recent results concerning the design and characterization of supersonic gas nozzles able to deliver such high densities and the first results obtained during the first experiment on PICO2000 facility at LULI. We succeeded to accelerate ions up to several MeV with a H2 and He gas jet target. The number of accelerated ions is comparable to the one usually obtained with solid targets.
The SEPAGE spectrometer (Spectromètre Electrons Protons A Grandes Energies) was realized within the PETAL+ project funded by the French ANR (French National Agency for Research). This plasma diagnostic, installed on the LMJ-PETAL laser facility, is dedicated to the measurement of charged particle energy spectra generated by experiments using PETAL (PETawatt Aquitaine Laser). SEPAGE is inserted inside the 10-meter diameter LMJ experimental chamber with a SID (Diagnostic Insertion System) in order to be close enough to the target. It is composed of two Thomson Parabola measuring ion spectra and more particularly proton spectra ranging from 0.1 to 20 MeV and from 8 to 200 MeV for the low and high energy channels respectively. The electron spectrum is also measured with an energy range between 0.1 and 150 MeV. The front part of the diagnostic carries a film stack that can be placed as close as 100 mm from the target center chamber. This stack allows a spatial and spectral characterization of the entire proton beam. It can also be used to realize proton radiographies.
The generation of energetic electrons by the interaction of a short laser pulse with solid “grating” targets, having a periodic groove on the irradiated surface, has been investigated in a regime of ultrahigh contrast (1012) and relativistically strong intensity (> 1019W/cm2). A strong enhancement of both the energy and number of electrons emitted from the target, with respect to at targets, has been observed for incidence angles close to the resonant condition for surface wave excitation. In particular we identified bunches of electrons with energies exceeding 10 MeV which are emitted in a direction close to the target surface. The experimental results are well reproduced by a three-dimensional particle-in-cell simulation, which confirms the dominant role of the surface wave in accelerating the electrons. These results are a step forward the development of high field plasmonics for a number of applications.
A. Sgattoni, T. Ceccotti, V. Floquet, A. Bigongiari, M. Raynaud, C. Riconda, F. Baffigi, L. Labate, L. Gizzi, L. Vassura, J. Fuchs, O. Klimo, M. Kveton, F. Novotny, M. Possolt, J. Prokupek, J. Proska, J. Psikal, L. Stolcova, A. Velyhan, M. Bougeard, P. Martin, I. Prencipe, A. Zani, D. Dellasega, A. Macchi, M. Passoni
Experimental results are reported for two different configurations of laser driven ion acceleration using solid foils with a structured layer on the irradiated side, aiming to improve the laser-target coupling by exploiting engineered surfaces. Two experimental campaigns have been performed exploiting a 100TW 25fs Ti:Sa laser capable of maximum intensity of 4 • 1019 W/cm2. ”Grating” targets have been manufactured by engraving thin mylar foils (0.9, 20 and 40 μm) with a regular modulation having 1.6 μm period and 0.5 μm depth. The periodicity of the grating corresponds to a resonant incident angle of 30° for the excitation of surface waves. Considering a target of 20 μm and changing the angle of incidence from 10° to 45°, a broad maximum in the proton energy cut-off was observed around the resonant angle (about 5 MeV) which was more than a factor two higher than the case of planar target. ”Foam” targets have been manufactured by depositing a porous 10 μm nanostructured carbon film with an average density of 1-5 mg/cm3 on a 1 μm thick aluminium foil. At maximum focalization the foam targets gave a maximum proton energy similar to the case of bare aluminium target (about 6 MeV), while educing the intensity the presence of the foam enhanced the maximum proton energy, obtaining about 1.5MeV vs. 500KeV at an intensity of 5 • 1016 W/cm2. 2D Particle-In-Cell simulations have been used to support the intepretation of the experimental results.
Interaction of an ultra-short intense laser pulses with thin foil targets is accompanied by acceleration of ions from the
target surface. To make this ion source suitable for applications, it is of particular importance to increase the efficiency
of laser energy transformation into accelerated ions and the maximum ion energy. This can be achieved by using thin foil
target with a layer of microscopic spheres on the front, laser irradiated surface. The influence of microscopic structure on
the target surface on the laser target interaction and subsequent ion acceleration is studied here using numerical
simulations. The influence of the size of microspheres, the density profile and the laser pulse incidence angle are studied
as well.
Ph. Martin, G. Doumy, M. Servol, M. Bougeard, H. Stabile, S. Dobosz, P. Monot, F. Quéré, F. Réau, P. d'Oliveira, H. Lagadec, T. Ceccotti, P. Audebert, J. Geindre, S. Hüller
By focusing an intense femtosecond, high temporal contrast, laser on ultra-thin foils (100 nm) in the 1018W/cm2 intensities range, we demonstrate that we create instantaneously a hot solid-density plasma. The use of highorder harmonics generated in a gas jet, providing a probe beam of sufficiently short wavelengths to penetrate in such media, enables to study the dynamics of this plasma on the picosecond time-scale. The comparison of the transmission of two successive harmonics permits to determine the electronic density and the temperature with an accuracy better than 15% never achieved up to date in relativistic regimes.
According to the ISMT roadmap, Extreme Ultraviolet lithography (EUVL) is the most promising technology to reach the 45-nm node for industrial production and to satisfy the famous law of Moore beyond 2007. Already in 1998 the first European EUVL project (EUCLIDES) has been launched under the leadership of ASM Lithography. Shortly after that in 1999, the national R&D program PREUVE started in France to improve EUVL related technologies and to build the first experimental lithography bench (BEL) in Europe. Finally, in 2001, the main European industrial companies as well as academic and national laboratories have federated within the important MEDEA+ effort to overcome the main technological challenges and to industrialize EUVL in time. Indeed, one of the most important challenges of EUVL concerns the achievement of very powerful, clean and reliable sources. The present paper will give the current state of European EUVL source technology and an overview of the different approaches. Main results are reviewed and the remaining challenges are discussed.
Within the PREUVE project, the GAP of CEA Saclay has developed an EUV source that should meet (alpha) -tool specifications by the end of this year. In particular, a laser-produced plasma source has been developed that uses a dense and confined xenon jet target. Our technical solution is based on a specific target injector design and the use of well adapted nozzle materials to avoid debris formation by plasma erosion. After injection, the xenon is recycled and highly purified to reach a low cost round- the-clock operation. This source provides both high conversion efficiency and low debris flux. These are necessary conditions for its industrial application in the future EUV microlithography. The conception of the so-called ELSA (EUV Lithography Source Apparatus) prototype allows in principal 2 years full operation on the French lithography test bench BEL (Banc d'essai pour la lithographie) that has been developed during PREUVE. In parallel, the EXULITE consortium that is coordinated by Alcatel Vacuum Technology France (AVTF) has started its activities in the frame of the European MEDEA+ initiative on EUV source development. In collaboration with Thales and the CEA, AVTF develops a prototype power source for EUV lithography production tools by the end of 2004. A low cost and modular high power laser system architecture has been chosen and is developed by Thales and the CEA to pump the laser plasma- produced EUV source.
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