Peer-reviewed Publications |
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Atabek, O., & Lefebvre, R. (2008). Multiple occurrence of zero-width resonances in photodissociation: Effect of laser field intensity and frequency. PHYSICAL REVIEW A, 78(4), 043419.
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Casagrande, E. M. S., Naja, A., Mezdari, F., Lahmam-Bennani, A., Bolognesi, P., Joulakian, B., Chuluunbaatar, O., Al-Hagan, O., Madison, D. H., Fursa, D. V., & Bray, I. (2008). (e,2e) ionization of helium and the hydrogen molecule: signature of two-centre interference effects. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 41(2).
Résumé: Relative (e,2e) triply differential cross sections (TDCS) are measured for the ionization of the helium atom and the hydrogen molecule in coplanar asymmetric geometry at a scattered electron energy of 500 eV and ejected electron energies of 205, 74 and 37 eV. The He experimental results are found to be in very good agreement with convergent close-coupling calculations (CCC). The H(2) experimental results are compared with two state-of-the-art available theoretical models for treating differential electron impact ionization of molecules. Both models yield an overall good agreement with experiments, except for some intensity deviations in the recoil region. Similar (e, 2e) works were recently published on H(2) with contrasted conclusions to the hypothesis that the two H nuclei could give rise to an interference pattern in the TDCS structure. Murray (2005 J. Phys. B: At. Mol. Opt. Phys. 38 1999) found no evidence for such an effect, whereas Milne-Brownlie et al (2006 Phys. Rev. Lett. 96 233201) reported its indirect observation. In this work, based on a direct comparison between experimental results for He and H(2), we observe an oscillatory pattern due to these interference effects, and for the first time the destructive or constructive character of the interference is observed, depending on the de Broglie wavelength of the ejected electron wave. The experimental finding is in good agreement with the theoretical prediction by Stia et al (2003 J. Phys. B: At. Mol. Opt. Phys. 36 L257).
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Charron, E., Milman, P., Keller, A., & Atabek, O. (2008). Erratum: Quantum phase gate and controlled entanglement with polar molecules [Phys. Rev. A 75, 033414 (2007)]. PHYSICAL REVIEW A, 77(3), 039907.
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Colgan, J., Huetz, A., Reddish, T. J., & Pindzola, M. S. (2008). Internuclear separation dependence of the angular distributions from photoionization of H(2)(+). JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 41(8).
Résumé: Recent experimental and theoretical works examining the double photoionization of H(2) have uncovered surprising changes in the resulting fully differential cross sections as the kinetic energy released to the outgoing protons is varied. In this work, a complementary study is made of the angular distributions arising from the photoionization of H(2)(+) at various internuclear separations R. Different internuclear separations correspond to different amounts of kinetic energy released to the exploding protons. We find that the angular distributions for the sigma(g) --> pi(u) transition in H(2)(+) are relatively insensitive to changes in R, but that the angular distributions for the sigma(g) --> pi(u) transition display dramatic variations with R. We investigate the underlying mechanisms of these phenomena, and explore the implications of these findings for the double photoionization of H(2).
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Guyetand, O., Gisselbrecht, M., Huetz, A., Agostini, P., Carre, B., Breger, P., Gobert, O., Garzella, D., Hergott, J. - F., Tcherbakoff, O., Merdji, H., Bougeard, M., Rottke, H., Boettcher, M., Ansari, Z., Antoine, P., & DiMauro, L. F. (2008). Complete momentum analysis of multi-photon photo-double ionization of xenon by XUV and infrared photons. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 41(6).
Résumé: Photo-double ionization (PDI) of xenon by the Ti: Sapphire laser fundamental frequency combined to its 19th and 25th harmonics has been studied by means of a momentum imaging spectrometer. The measurement of the two emitted photoelectrons' momenta and their energy and angular correlations gives insight into the various mechanisms leading to PDI. Although the conditions for non-sequential direct photo-double ionization are fulfilled in the experiment, it is found that the two-step processes dominate.
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Guyetand, O., Gisselbrecht, M., Huetz, A., Agostini, P., Taieb, R., Maquet, A., Carre, B., Breger, P., Gobert, O., Garzella, D., Hergott, J. - F., Tcherbakoff, O., Merdji, H., Bougeard, M., Rottke, H., Boettcher, M., Ansari, Z., & Antoine, P. (2008). Evolution of angular distributions in two-colour, few-photon ionization of helium. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 41(5).
Résumé: Single ionization of helium by a superposition of selected XUV high harmonics and infrared radiation has been studied by a momentum imaging technique. The measured angular distributions of photoelectrons are compared to numerical time- dependent calculations, showing very good agreement after average. The calculated angular distributions appear to depend critically on the delay between harmonic and infrared pulses on the attosecond scale, and on the relative phases and intensities of the harmonics.
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Journel, L., Guillemin, R., Haouas, A., Lablanquie, P., Penent, F., Palaudoux, J., Andric, L., Simon, M., Ceolin, D., Kaneyasu, T., Viefhaus, J., Braune, M., Li, W. B., Elkharrat, C., Catoire, F., Houver, J. - C., & Dowek, D. (2008). Resonant double Auger decay in carbon K-shell excitation of CO. PHYSICAL REVIEW A, 77(4).
Résumé: We have studied double Auger decay after C 1s -> 2 pi(*) photoexcitation in gas phase carbon monoxide. Two distinct processes, namely direct double Auger decay and cascade double Auger decay, are identified and studied in detail using multiple coincidence techniques. Cascade Auger decay is shown to be the overall dominant process. Decay channels involving the dissociation of the molecule followed by autoionization of the oxygen fragments are observed.
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Kazamias, S., Cassou, K., Ros, D., Ple, F., Jamelot, G., Klisnick, A., Lundh, O., Lindau, F., Persson, A., Wahlstroem, C. - G., de Rossi, S., Joyeux, D., Zielbauer, B., Ursescu, D., & Kuehl, T. (2008). Characterization of a transient collisional Ni-like molybdenum soft-x-ray laser pumped in grazing incidence. PHYSICAL REVIEW A, 77(3), 033812.
Résumé: We present experimental results from an extensive investigation of a Ni-like Mo x-ray laser pumped in the transient regime and GRIP configuration (GRazing Incidence Pumping). The pump laser is a 10 Hz, 1 J, Ti: sapphire laser system. The main diagnostic is a monochromatic near-field imaging system with a 1.7 micron spatial resolution that shows the soft-x-ray laser source size and position relative to the target surface. Changes of those characteristics are observed for different GRIP angles, varied between 15 and 21, while keeping all other parameters constant. Intense lasing is observed routinely at 18.9 nm with up to 3 microjoule output energy and stable operation is demonstrated at 10 Hz. We have investigated the role of several pumping parameters, in particular, the relative energy and delay between the long and short pulse. We show that this multiparameter scan leads to a well-defined optimal regime of operation and better understanding of the GRIP configuration. Finally, as the GRIP scheme requires careful tailoring of the plasma conditions to the specific soft-x-ray laser under investigation, we add a prepulse before the plasma producing long pulse to generate large-scale preplasmas. This increases the brightness of the soft-x-ray beam and leads to an almost Gaussian near-field spatial profile.
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Kheifets, A. S., Naja, A., Casagrande, E. M. S., & Lahmam-Bennani, A. (2008). DWBA-G calculations of electron impact ionization of noble gas atoms. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 41(14).
Résumé: We perform calculations of electron impact ionization of noble gas atoms within the distorted wave Born approximation (DWBA) corrected by the Gamow factor (G) to account for the post-collision interaction. We make an extensive comparison with experimental data on He 1s(2), Ne 2s(2), 2p(6) and Ar 3p(6) under kinematics characterized by large energy transfer and close to minimum momentum transfer from the projectile to the target. For all atoms, good agreement between theory and experiment is achieved. In the case of Ar, the disagreement of experimental data with theory reported earlier by Catoire et al (2006 J. Phys. B: At. Mol. Opt. Phys. 39 2827) is reconciled.
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Le Padellec, A., Lievin, J., Staicu-Casagrande, E. M., Nzeyimana, T., Naji, E. A., & Urbain, X. (2008). Competitive processes in the associative ionization of C- with C+, N+, and O+. PHYSICAL REVIEW A, 78(6).
Résumé: Absolute integral cross sections have been measured for associative ionization reactions involving the C- and C+, N+, and O+ reactants. These measurements, obtained using a merged-beam setup in the keV range, provide us with useful experimental information on the efficiency and mechanisms of molecular ion formation from ionic reactants. The relative magnitudes of the different cross sections are rationalized by considering the spin multiplicities of initial and final states, and the exothermicities of the detachment and transfer ionization channels. The very different production efficiencies of CO+ ions via the O-+C+ and C-+O+ channels are explained by statistical and energetic considerations. The potential energy curves of CO and CO+ have been calculated by quantum ab initio methods in order to characterize the reactive pathways leading to autoionization. Thermal rate coefficients are derived to serve the plasma physics community.
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Meyer, M., Cubaynes, D., Glijer, D., Dardis, J., Hayden, P., Hough, P., Richardson, V., Kennedy, E. T., Costello, J. T., Radcliffe, P., Duesterer, S., Azima, A., Li, W. B., Redlin, H., Feldhaus, J., Taieb, R., Maquet, A., Grum-Grzhimailo, A. N., Gryzlova, E. V., & Strakhova, S. I. (2008). Polarization Control in Two-Color Above-Threshold Ionization of Atomic Helium. PHYSICAL REVIEW LETTERS, 101(19), 193002.
Résumé: Two-color multiphoton ionization of atomic helium was investigated by combining extreme ultraviolet (XUV) radiation from the Free Electron Laser in Hamburg with an intense synchronized optical laser. In the photoelectron spectrum, lines associated with direct ionization and above-threshold ionization show strong variations of their amplitudes as a function of both the intensity of the optical dressing field and the relative orientation of the linear polarization vectors of the two fields. The polarization dependence provides direct insight into the symmetry of the outgoing electrons in above-threshold ionization. In the high field regime, the monochromaticity of the XUV radiation enables the unperturbed observation of nonlinear processes in the optical field.
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Naja, A., Casagrande, E. M. S., Lahmam-Bennani, A., Stevenson, M., Lohmann, B., Dal Cappello, C., Bartschat, K., Kheifets, A., Bray, I., & Fursa, D. V. (2008). (e, 2e) triple differential cross-sections for ionization beyond helium: the neon case at large energy transfer. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, 41(8).
Résumé: We report new coplanar (e, 2e) results for ionization of the He 1s and Ne 2p and 2s subshells under kinematics which have remained rather unexplored to date and characterized by large energy transfer and close to minimum momentum transfer from the projectile to the target. The experimental results obtained in two laboratories are used as a sensitive test of a number of state-of-the-art available theoretical models for multi-electron atoms. The He results are in excellent agreement with convergent close-coupling predictions as well as with distorted-wave + Gamow and hybrid distorted-wave + R-matrix models. In the Ne case, an overall satisfactory agreement with experiments is obtained for all considered models. The importance of post-collisional interaction effects is demonstrated whereas second-order effects in the projectile-target interaction at small distances are shown to be negligibly small. Remaining discrepancies between theories and experiments are discussed.
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Reddish, T. J., Colgan, J., Bolognesi, P., Avaldi, L., Gisselbrecht, M., Lavollee, M., Pindzola, M. S., & Huetz, A. (2008). Physical interpretation of the “kinetic energy release” effect in the double photoionization of H(2). PHYSICAL REVIEW LETTERS, 100(19), 193001.
Résumé: A physical interpretation is given for the variation with internuclear separation of the fully differential cross section for double photoionization of H2. This effect is analyzed in a geometry where the fourbody interaction is completely probed. Excellent agreement is found between experiment and time-dependent close-coupling theory after convoluting the latter over the relevant solid angles. We show the observed variations are purely due to the epsilon(Sigma) component of the polarization vector epsilon along the molecular axis, a conclusion which is supported through calculations of the photoionization of H2(+).
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Saugout, S., Charron, E., & Cornaggia, C. (2008). H2 double ionization with few-cycle laser pulses. PHYSICAL REVIEW A, 77, 023404.
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Thissen, R., Bizau, J. M., Blancard, C., Coreno, M., Dehon, C., Franceschi, P., Giuliani, A., Lemaire, J., & Nicolas, C. (2008). Photoionization cross section of Xe(+) ion in the pure 5p(5) (2)P(3/2) ground level. PHYSICAL REVIEW LETTERS, 100(22), 223001.
Résumé: Coupling an ion trap with synchrotron radiation is shown here to be a powerful approach to measure photoionization cross sections on ionic species relaxed in their ground state. The photoionization efficiency curve of Xe(+) ions stored in a Fourier transform ion cyclotron resonance ion trap was recorded at ELETTRA in the 20-23 eV photon energy range. Absolute cross sections were derived by comparison of the photoionization yield of Xe(+) with measurements from the ASTRID merged-beam experiment. Multiconfiguration Dirac-Fock calculations were performed for the interpretation of these new data.
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Actes de Conférences |
Elkharrat, C., Picard, Y. J., Billaud, P., Houver, J. C., & Dowek, D. (2008). Electron-ion vector correlations for the study of photoionization of molecules in the UVX range: From synchrotron radiation to short light pulses. In UVX 2008: 9E COLLOQUE SUR LES SOURCES COHERENTES ET INCOHERENTES UV (pp. 35–43).
Résumé: Molecular frame photoemission is a very sensitive probe of the photoionization (PI) dynamics of molecules. The electron-ion vector correlation (VC) method takes advantage of dissociative photoionization (DPI) reactions of small molecules to measure such observables. It relies on the coincident detection of the photoelectron and the ion fragment emitted from the same DPI event and the determination of their velocity vectors. Most of the VC studies so far have been performed using synchrotron radiation (SR) light sources which benefit from a high repetition rate (1-10 MHz) favorable for coincidence experiments. In this paper we discuss the extension of this method to the study of PI processes induced by ultra-short VUV light sources, which provide the capability for investigating processes characterized by femtosecond or subfemtosecond dynamics. We first illustrate the VC method by the report of recent results of a comparative study of resonant photoionization of the H(2) and D(2) molecules induced by VUV circularly polarized synchrotron radiation at SOLEIL in the region involving resonant excitation of Q(1) and Q(2) doubly excited state series. This problem is of particular interest since autoionization and dissociation of selected Q, or Q(2) states occur on a comparable time scale of few femtoseconds, which implies a coupling between the electronic and nuclear motion. The extension of the VC method using femtosecond laser sources is then demonstrated by results for multiphoton PI of the Xe atom induced by 70 fs pulses centered at 400 nm delivered by the SOFOCKLE and PLFA Sources (SLIC, CEA-Saclay) after frequency doubling of a 1 kHz Ti:sapphire laser.
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Goddet, J. - P., Sebban, S., Guilbaud, O., Maynard, G., Cros, B., Gautier, J., Zeitoun, P., Valentin, C., Tissandier, F., Marchenko, T., Lambert, G., Benredjem, D., Boudaa, A., Klisnick, A., Ros, D., Kazamias, S., Cassou, K., Habib, J., Jamelot, G., Lagron, J. - C., Joyeux, D., De Rossi, S., Phalippou, D., Delmotte, F., Ravet, M. F., Calisti, A., Mocek, T., Kozlova, M., & Jakubczak, K. (2008). Spatio-temporal characterization of an injected XUV laser. In UVX 2008: 9E COLLOQUE SUR LES SOURCES COHERENTES ET INCOHERENTES UV (pp. 51–56).
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Guilbaud, O., Ros, D., Kazamias, S., Zielbauer, B., Habib, J., Pittman, M., Cassou, K., Ple, F., Farinet, M., Klisnick, A., de Dortan, F., Lacombe, S., Porcel, E., Le Sech, C., du Penhoat, M. - A., Touati, A., Marsi, M., Fajardo, M., Zeitoun, P., & Joyeux, D. (2008). LASERIX: first record from the plant. In UVX 2008: 9E COLLOQUE SUR LES SOURCES COHERENTES ET INCOHERENTES UV (pp. 57–63).
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Habib, J., Klisnick, A., Guilbaud, O., Joyeux, D., Zielbauer, B., Kazamias, S., Pittman, M., Ros, D., & de Dortan, F. (2008). Temporal coherence and spectral linewidth of XUV transitory lasers pumped in grazing incidence. In UVX 2008: 9E COLLOQUE SUR LES SOURCES COHERENTES ET INCOHERENTES UV (pp. 157–161).
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