Publications

1998

• Contrôle et mise en forme des fronts de phase et d'énergie d'impulsions brèves ultra-intenses
  
  • Chanteloup Jean-Christophe
  , 1998. Ce mémoire de thèse traite du contrôle et de la mise en forme des fronts de phase et d'énergie d'impulsions lasers brèves ultra-intenses. La première partie est consacrée à la conception et la réalisation d'une boucle d'optique adaptative pour la correction des distorsions de surface d'onde sur la chaîne laser de puissance 100 Térawatts du Laboratoire pour l'Utilisation des Lasers Intenses. Cette boucle repose sur l'utilisation d'un dispositif à cristaux liquides comme modulateur de phase et d'un interféromètre à décalage comme senseur de front d'onde. L'association de ces deux dispositifs a permis la construction d'un système innovant de mesure et mise en forme de la surface d'onde d'impulsions lasers ultra-intenses. Il est démontré qu'il permet de corriger une surface d'onde présentant d'importantes distorsions et ainsi améliorer grandement la qualité de focalisation de faisceaux lasers. Cette boucle d'optique adaptative a été testée avec succès sur la chaîne 100 Térawatts et une correction de la surface d'onde de l'ordre de 60% a ainsi pu être démontrée. La seconde partie du mémoire traite de la mise en forme d'une impulsion laser inhomogène brève permettant le pompage du milieu à gain (un plasma) d'un laser à rayons X. L'idée consiste à jouer sur le parallélisme du système de compression d'impulsions utilisé en fin de chaîne 100 Térawatts. Un modèle expliquant la génération d'une impulsion inhomogène laser brève à l'aide de ce compresseur à réseaux de diffraction est développé. Une campagne expérimentale Laser X a notamment permis de valider les prédictions théoriques annoncées par ce modèle et a montré la nécessité d'utiliser une telle impulsion inhomogène afin d'obtenir une émission laser X lorsque le pompage s'effectue par impulsion brève.
• Detection of point mutations associated with resistance of Helicobacter pylori to clarithromycin by hybridization in liquid phase.
  
  • Pina M.
  • Occhialini A.
  • Monteiro L
  • Doermann H
  • Mégraud F.
  Journal of Clinical Microbiology, American Society for Microbiology, 1998, 36 (11), pp.3285-90. When the standard procedure for determining antibiotic susceptibility of bacteria is used, the results are delayed, especially for bacteria that grow slowly, such as Helicobacter pylori. Treatment for this bacterium may involve clarithromycin, a compound for which resistance has been associated with point mutations on the 23S rRNA gene. This resistance is currently found in organisms isolated from 0 to 15% of patients and jeopardizes the success of the treatment. We have designed a test involving amplification and colorimetric hybridization in the liquid phase to detect the mutation at the molecular level. First, four reference strains, including the wild type and three strains with the mutations A2143C, A2143G, and A2144G, were used to optimize the method. Amplification was carried out with primers previously published. The amplified products were added to probe-coated microtiter wells. A DNA enzyme immunoassay was used to detect the hybrids. The optimal conditions of the hybridization were defined for each probe. Nineteen H. pylori strains resistant to clarithromycin and 22 susceptible according to phenotypic data were submitted to restriction with BsaI and BbsI, and part of the 23S rRNA gene was sequenced in order to determine the mutation involved for the resistant strains. The new assay showed a complete correlation with the reference methods, except for one strain. Cross-hybridizations as well as application of the reaction to other bacteria did not lead to optical densities higher than the cutoff values chosen with the receiving operating characteristic curve. This method can be easily standardized and gives a result within a day. Its application directly to the biopsy specimens or infected gastric juice is planned in the future.
• Observation of laser wakefield acceleration of electrons
  
  • Amiranoff François
  • Baton S.
  • Bernard D.
  • Cros B.
  • Descamps D.
  • Dorchies F.
  • Jacquet F.
  • Malka Victor
  • Marquès J. R.
  • Matthieussent G.
  • Miné P.
  • Modena A.
  • Mora P.
  • Morillo J.
  • Najmudin Z.
  Physical Review Letters, American Physical Society, 1998, 81 (5), pp.995. The acceleration of electrons injected in a plasma wave generated by the laser wakefield mechanism has been observed. A maximum energy gain of 1.6 MeV has been measured and the maximum longitudinal electric field is estimated to 1.5 GV/m. The experimental data agree with theoretical predictions when 3D effects are taken into account. The duration of the plasma wave inferred from the number of accelerated electrons is of the order of 1 ps (10.1103/PhysRevLett.81.995)
  DOI : 10.1103/PhysRevLett.81.995
• Plasma Wave Generation in a Self-Focused Channel of a Relativistically Intense Laser Pulse
  
  • Clayton C. E.
  • Tzeng K.-C.
  • Gordon D.
  • Muggli P.
  • Mori W. B.
  • Joshi C.
  • Malka Victor
  • Najmudin Z.
  • Modena A.
  • Neely D.
  • Dangor A. E.
  Physical Review Letters, American Physical Society, 1998, 81 (1), pp.100. Evidence for self-channeling of a relativistically intense laser pulse in an underdense plasma is presented through Schlieren and 90° Thomson sidescatter images. Using collective Thomson scattering of a probe beam, we observe that relativistically propagating plasma waves are excited over the entire length of the channel, up to 12 Rayleigh lengths (≈4mm). From the wave amplitude, the intensity inside the channel is estimated to be ∼1018W/cm2. (10.1103/PhysRevLett.81.100)
  DOI : 10.1103/PhysRevLett.81.100
• Modeling the radiative properties of dense plasmas
  
  • Gauthier P
  • Rose Sj
  • Sauvan P
  • Angelo P
  • Leboucher-Dalimier E
  • Calisti Annette
  • Talin B
  Physical Review E, American Physical Society (APS), 1998, 58 (1), pp.942-950. A model aimed at describing the electronic structure of hot dense plasmas is presented. This model is first used to study the effect of the nearest neighbor interaction on the photoabsorption K-edge position in a dense fluorine plasma. Changes to the ionization potential lowering from the well-known ion sphere model [H. Nguyen er al., Phys, Rev, A 33, 1279 (1986)] are obtained by the present approach for plasma density above solid. We believe that this effect could be of importance in the calculation of the opacity of dense materials. The present model also provides an alternative to the treatment of line broadening in very dense plasmas where the average interionic spacing can be of the order of the spatial extent of the excited-state orbitals. To illustrate this point, we present F Lyman-beta line shapes for various density conditions. (10.1103/PhysRevE.58.942)
  DOI : 10.1103/PhysRevE.58.942
• The laser wakefield acceleration experiment at Ecole Polytechnique
  
  • Amiranoff François
  • Bernard D
  • Cros B
  • Dorchies F
  • Jacquet F
  • Malka Victor
  • Marques J.R
  • Matthieussent G
  • Mine Ph
  • Modena A
  • Morillo Joseph
  • Najmudin Z
  Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Elsevier, 1998, 410 (3), pp.364. A laser wakefield electron acceleration experiment has been set-up at Ecole Polytechnique. An electron beam with 3 MeV total energy is injected in a plasma wave generated by laser wakefield using the new LULI CPA laser (400 fs [FWHM], I<1017 W/cm2). The first results show an effective acceleration of the order of 1 MeV, with a maximum when the electron density is close to the optimum value for which the laser pulse length is about half the plasma wavelength (10.1016/S0168-9002(98)00150-8)
  DOI : 10.1016/S0168-9002(98)00150-8
• Observation of Electron Energies Beyond the Linear Dephasing Limit from a Laser-Excited Relativistic Plasma Wave
  
  • Gordon D.
  • Tzeng K. C.
  • Clayton C. E.
  • Dangor A. E.
  • Malka Victor
  • Marsh K. A.
  • Modena A.
  • Mori W. B.
  • Muggli P.
  • Najmudin Z.
  • Neely D.
  • Danson C.
  • Joshi C.
  Physical Review Letters, American Physical Society, 1998, 80 (10), pp.2133. The spatial extent of the plasma wave and the spectrum of the accelerated electrons are simultaneously measured when the relativistic plasma wave associated with Raman forward scattering of an intense laser beam reaches the wave breaking limit. The maximum observed energy of 94 MeV is greater than that expected from the phase slippage between the electrons and the accelerating electric field as given by the linear theory for preinjected electrons. The results are in good agreement with 2D particle-in-cell code simulations of the experiment. (10.1103/PhysRevLett.80.2133)
  DOI : 10.1103/PhysRevLett.80.2133
• Two-centre bound states in hot dense plasmas
  
  • Gauthier P
  • Sauvan P
  • Angelo P
  • Alexiou S
  • Leboucher-Dalimier E
  • Poquerusse A
  • Calisti Annette
  • Talin B
  Laser and Particle Beams, Cambridge University Press (CUP), 1998, 16 (1), pp.39-43. A model for describing the transient molecular behavior in hot dense plasmas is presented and applied to the case of a transient F8+/F9+ molecular ion embedded in a dense (N-e approximate to 10(23) cm(-3)) fluorine plasma. Electron screening effects on molecular energy levels and on dipolar matrix elements are investigated for specific plasma conditions. The accuracy of the calculations is tested comparing values of the polarization shift of the FLy beta line as calculated from the present model to the ones determined in the framework of the Ion Sphere Model (ISM). (10.1017/S0263034600011757)
  DOI : 10.1017/S0263034600011757
• Laser wakefield: Experimental study of nonlinear radial electron oscillations
  
  • Marques J. R.
  • Dorchies F.
  • Amiranoff François
  • Audebert P.
  • Gauthier J. C.
  • Geindre J. P.
  • Antonetti A.
  • Antonsen T. M.
  • Chessa P.
  • Mora P.
  Physics of Plasmas, American Institute of Physics, 1998, 5 (4), pp.1162-1177. no abstract
• Efficient generation of narrow-bandwidth picosecond pulses by frequency doubling of femtosecond chirped pulses
  
  • Raoult F.
  • Boscheron A. C. L.
  • Husson D.
  • Sauteret C.
  • Modena A.
  • Malka Victor
  • Dorchies F.
  • Migus A.
  Optics Letters, Optical Society of America - OSA Publishing, 1998, 23 (14), pp.1117. We demonstrate efficient generation of picosecond narrow-bandwidth pulses by frequency mixing of broadband opposite chirped pulses in a type I doubling crystal. This procedure allows us to produce picosecond pulses that are perfectly synchronized with femtosecond pulses. The experiment shows a decrease of the initial bandwidth by a factor of more than 30, while a high conversion efficiency is maintained (10.1364/OL.23.001117)
  DOI : 10.1364/OL.23.001117