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Porte-parole : Laurent Nahon, SPAM/DRECAM-CEA et L.U.R.E.
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 Scientific programme
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With a unique combination of ultra high resolution (200000 Resolving Power) and flux (9m undulator) in the VUV range ( 5-40 eV), this beamline will provide totally new opportunities for photophysics and photochemistry studies on dilute samples. The availability of versatile (linear, circular) polarisation characteristics of the photon beam is a specificity of the proposal allowing dichroic and chirality studies. This energy range is the domain in which photon-induced processes involve the valence shell electrons. This is a common characteristics to the different scientific topics proposed for the present beamline at SOLEIL. These topics can be roughly classified into 5 different categories - High resolution spectroscopy : the high resolution branch, or the Fourier-transformed projected arm for ultra-high resolution (1/400000), is used to identify the electronic, vibrational and rotational levels of excited cold molecules, radicals, clusters and solid compounds. Besides the spectroscopic aspect in itself, structural informations are gathered as well as absolute cross sections which are extremely valuable for atmospheric and astrophysics related systems. The reduction, analysis, interpretation of astronomical or atmospherical observations data and the construction of sophisticated theoretical models require at each stage increasingly extensive sets of laboratory atomic and molecular data. This is even true for the well-studied and simple diatomic molecule CO (and its isotopic forms) but the need still exists for many other molecules observed in the interstellar medium or in planetary atmospheres (N2, SO2, O2 SO2, NH3, C2H2, …). These studies may use ion/electron/fluorescence or absorption spectroscopy and require of course high-resolution capabilities as well as high flux in the case of very dilute samples.
- Molecular dynamics and reactivity : VUV photons are used to either induce a chemical reaction via a chemical bond breaking, such as in the photodissociation or photodesorption processes (half-collision), or to prepare reactants such as selected-energy ions that can react with neutrals, with, in addition, fixed impact parameters if this collision takes place in a Van der Waals aggregate. The targets may be molecules adsorbed on surfaces or molecular aggregates. Most of these studies use ion yield and mass spectroscopies often associated with threshold electron spectroscopy in a coincidence scheme. They require a high spectral purity (no transmitted higher orders) and sometimes flux associated with a moderate to high resolution. In addition, the use of a synchronized pulsed laser (conventional or FEL) could bring direct informations on molecular dynamics in the temporal domain (micro-seconds to tens of pico-seconds dynamics), via the performance of pump-probe experiments.
- Photoionization dynamics : one is here mostly interested in the spectroscopy and relaxation dynamics such as autoionization and fluorescence decay of highly excited state of neutrals as well as of satellites electronic excited states of the ion converging towards the second ionisation limit. Many studies will rely on state-selected ion production and high resolution threshold photoelectron spectroscopy by the ZEKE/MATI field ionisation techniques.
Experimental techniques are based on different electron/ion spectroscopies often in a coincidence scheme, requiring in general a high flux in a rather small photon bandwidth. Such studies can be performed by using one and two-color schemes, involving then a laser photon in addition to the SR one, in order to look to parity-related effects for instance. |
- Molecular alignment, dichroism and chirality : this is the core of the large scientific case dealing with the use of variable polarizations such as rotating linear and circular polarizations. The basic idea is to either induced or probe an alignment or some anisotropy in a system by the use of VUV SR light with a given and well-defined polarization. This very large topic, of interest for molecular physics, chemistry, and biology relies on the use of very different experimental techniques relevant to both the gas and the condensed phase, but all require the use of variable, well-controlled and measured polarization state. The main issues are listed below:
- Vector Correlations in Dissociative Photoionization of simple molecules
- Dichroism in the photoionization of laser-polarized species in the gas phase
- Circular dichroism (CDAD) in the photoionization of small chiral molecules in the gas phase
- Exobiology and chirality
- Chirality of organic molecules
- Photodissociation studied by polarized fluorescence
- Dichroism in the photoionization of molecules adsorbed on surfaces
- Absorption spectroscopy on Van der Waals chiral complexes
- Linear and circular dichroism in magnetic compounds
- Excitation and relaxation in the condensed phase : following the excitation in the VUV range in the solid or liquid phase, the subsequent relaxation mechanisms are probed by both frequency-resolved (absorption spectroscopy mainly) and time-resolved experiments in the microsecond to nanosecond range.
This field of research concerns primarily luminescent solids (scintillation efficiency and quenching, radiation hardness). The mentioned properties are governed by fundamental processes of the electron relaxation in the crystal after absorption of the photon energy with different characteristic times : (I) time range from 100 fs to 100 ps – typical times for electron-electron and electron-phonon scatterings, which control the mechanisms of creation of secondary excitations, localization of these excitations and defect formation; (II) time range from 100 ps to 100 ns – typical times for dipole-dipole transfer of the localised electron excitations and their recombination, which control the mechanisms of energy transfer to the fluorescence center and fuorescence emission; (III) time range from 100 ns to 1 s – typical times for thermal release of localized excitations from deep traps, which controls the phosphorence process (afterglow).
Evidently, investigation of these processes requires availability of pulsed sources for crystal excitation, the timing characteristics of which correspond to one or to several ranges.
Despite their fundamental interest, such studies have an evident applied goal which should attract industrial involvement specially in the field of detectors.
Another field is concerned with photoionisation of molecular crystals and liquids. Most of the interactions of high-energy particles with dense organic matter involve electronic excitations endowed with large oscillator strengths in the vacuum ultraviolet spectral range. While these excitations are relatively well known from the researches on the gas phase, some fundamental questions remain on their relaxation, in particular in liquids where specific dense phase processes appear, such as excitation and charge transfers to the coupled neighbours. The understanding of these mechanisms is a long lasting problem in radiation physics, chemistry and biology researches .
These experiments require flux over a large photon energy range, with also a good spectral purity.
The promoters have estimated that the scientific topics using the temporal structure of the ring operation represent about 50 % of the beamline programme.
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Communauté concernée
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| LURE (Orsay) : | C. Alcaraz, D. Cubaynes, P. Lablanquie, M. Meyer, F. Sirotti, A. Taleb, F. Polack, C. Laffon, P. Parent, R. Belkhou, F. Bertran | | IOTA (Orsay) : | D. Joyeux | | LCP (Orsay) : | O. Dutuit, R. Thissen | | LCAM (Orsay) | D. Dowek, J.C. Houver, P.M. Guyon | | LSAI (Orsay) : | A. Huetz | | LPPM (Orsay) | M. Vervloet
C. Jouvet, C. Dedonder-Lardeux, S. Martranchard
D. Gauyacq, N. Shafizadeh, S. Douin
G. Dujardin, L. Hellner, G. Comtet ,
A. Zehnaker, F. Lahmani, K. Le Barbu | | SPAM/LFP (CEA Saclay) : | L. Nahon, I. Dimicoli, M. Mons, F. Piuzzi, , M. Elhanine,
B. Soep, J.P. Visticot
| | LDIAM (Paris) : | R. Hall, F. Penent | | Observatoire de Meudon : | F. Rostas, S. Leach | | Université de Cergy-Pontoise : | J.L. Lemaire, J.-H. Fillon et coll. | | Lab. Aimé Cotton (Orsay) : | P. Cahuzac | | Ecole Polytechnique (Palaiseau) : | H.E. Audier et coll. | | ICSN (Gif sur Yvette) : | O. Laprévote | | IAS (Orsay) : | L. d’Hendecourt et coll. | | IPN (Orsay) : | J.C. Krupa et coll. | | Lab. Physico-chimie des Solides (Orsay) : | B. Poumellec | | IRES (Strasbourg) : | J.M. Jung, H. Gress | | Université de Lyon : | C. Pédrini et coll. | | Centre de Biophysique Moléculaire (Orléans) : | B. Barbier, A. Brack | | LISA (Créteil) : | M.C. Gazeau, Y. Benilan, A. Jolly, F. Rollin | | CELIA (Bordeaux) : | P. Martin, A. Belsky | | Université de Rennes 1 (PALMS) (Rennes) : | B. Mitchell | | Université de Lettonie (Riga, Lettonie) : | A. Trukkhin | | Institute of Nuclear Physics (Moscow, Russia) : | A. Grum-Grzhimailo | | University of Leiden (Pays-Bas) : | M. Greenberg | | University of Nottingham (UK) : | I. Powis | | SRS- CLRC (Daresbury, UK) : | E. Seddon |
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Recommandations du Comité Scientifique Consultatif (18-19 Nov. 2001)
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Proposal 7 (SU5 beamline at LURE-SACO) The SAC recommends the transfer of this beamline. The project is good and supported by a strong French community at the highest international level. The SAC asks however for some improvements of the proposal and suggests the following : - define the scientific priorities more explicitly and give a hierarchy in the project
- organise the proposed scientific board in an efficient wa
- the addition of a high resolution Fourier Transform spectrometer (side arm of the beamline) should be considered a priority. It uses the coherence of the source and gives the same energy resolution as laser
- a priority should also be given to two-colours experiments (coupling with laser sources and IR sources
The beamline scientists are advised to keep in close contact with the laser community in order to follow the new developments in the fie.
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Propositions de la Direction de SOLEIL
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La Direction de SOLEIL demande l’aval du Conseil pour le transfert de la ligne SU5 sur onduleur, avec les objectifs scientifiques et les caractéristiques générales exposés dans le projet.
Un effort de structuration de la communauté des utilisateurs doit être poursuivi. La réalisation du programme scientifique devra s’appuyer fortement sur les laboratoires associés, en particulier pour la mise en œuvre et l’ouverture sur la communauté, de montages expérimentaux spécifiques (montages CERISE pour l’étude des réactions chimiques élémentaires, TF pour la spectroscopie d’absorption haute résolution).
Le temps de faisceau proposé par SOLEIL en mode structure temporelle sera évalué après examen global du programme expérimental. Il sera établi dans une fourchette comprise entre 1100h. et 1650h. par an.
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