I. Yao-Leclerc, S. Brochet, C. Chauvet, N. De Oliveira, J.-P. Duval, J.-F. Gil, S. Kubsky, B. Lagarde, L. Nahon, F. Nicolas, M. Silly, F. Sirotti, M. Thomasset
Before the first photon beam was delivered at the SOLEIL synchrotron, scientists tried to anticipate the problem of
carbon contamination on optical components, with for instance the outgasing of chambers by prior exposure to the beam
with dummy optics. In spite of these efforts, deterioration of optical performance by carbon contamination has remained
an outstanding issue: on the low-energy beamlines at SOLEIL. For example, carbon contamination results in significant
photons flux losses (practically at the Carbon K edges), and modifications of the horizontal-to-vertical polarization
transmission ratio, which degrade with time as the thickness of the carbon layer builds up. This contamination is visible
and consists of a gray/black line over the entire photon beam footprint. Addressing the carbon contamination issue, two
cleaning processes have been tested quite successfully on two SOLEIL beamlines (in the UV-VUV and soft X-ray
ranges), namely in-situ oxygen plasma and in-situ ozone generation via UV lamps. A dedicated group is currently
working on the improvement of the cleaning processes, the metrology of the optics before and after cleaning and the
study of the carbon coating in order to propose possible strategies to prevent or slow down the contamination process.
Assuming an extra-terrestrial formation of life's molecular building blocks such as amino-acids, a possible abiotic
explanation for the selection of the L enantiomers could be the exposure to an asymmetric bias such as far UV Circularly
Polarized Light (CPL), during their journey towards Earth, inducing some enantiomeric excess (e.e) that could then be
amplified on Earth via suitable autocatalytic mechanisms. Synchrotron Radiation (SR), with its intense flux and broad
tunability, is a unique tool which mimics such an interstellar far UV CPL. We have recently employed it to study : (1)
The irradiation of solid films of the amino acid D,L-leucine, i.e. under relevant astrophysical conditions. Starting from
racemic D,L-leucine irradiated with CPL SR beam at 6.8 eV (182 nm), we have been able to induce by enantioselective
photolysis an e.e. of 2.6 %, as measured by chiral-sensitive CG-MS analysis, in accordance with the CD spectrum
recorded on the same type of sample. (2) CPL-induced gas phase photoionization of chiral molecules. By measuring the
angular distribution of photoelectrons ejected from pure enantiomers, we observed a strong anisotropy (up to 16 %) in
the forward/backward direction with respect to the light propagation axis. Because of momentum conservation, such an
effect is accompanied by an asymmetric recoil of the corresponding ions that could lead to a high e.e. Future prospects
on the new VUV SR beamline DESIRS at SOLEIL are presented.
We propose an accelerator based 4th generation source to provide coherent femtosecond light pulses down to the soft X
ray range to the user community. The project is based on a CW 700 MeV to 1 GeV superconducting linear accelerator
delivering high charge, subpicosecond, low emittance electron bunches with high repetition rate. This facility allows for
providing High Gain Harmonic Generation seeded with high harmonics in gases, covering a spectral range down to
0.8 nm. In addition, two beam loops are foreseen to increase the beam current in using the energy recovery technique.
They will accommodate fs synchrotron radiation sources in the IR, VUV and X ray ranges together with a FEL oscillator
in the 10 nm range. A particular emphasis is put on the synergy between accelerator and laser communities. In particular,
electron plasma acceleration will be tested. Hard X ray femtosecond radiation will be produced by Thomson Scattering.
The first phase of the project, ARC-EN-CIEL phase 1, is now under study. A general overview is given.
G. Lambert, B. Carre, M. Couprie, M. Desmons, O. Chubar, B. Gilquin, D. Garzella, M. Jablonka, M. Labat, A. Loulergue, J. Marques, J. Ortega, F. Meot, P. Monot, A. Mosnier, L. Nahon, A. Rousse
The French project of a fourth generation light source, ARC-EN-CIEL (Accelerator-Radiation for Enhanced Coherent Intense Extended Light), is a unique facility providing the user community with coherent femtosecond light pulses covering the UV, VUV and soft X ray spectral range. It is based on a CW 1 GeV superconducting linear accelerator delivering high charge, subpicosecond, low emittance electron bunches with high repetition rate (1 kHz), and adjustable polarisation until 1 keV. In addition to the High Gain Harmonic Generation (HGHG) experiment seeded with High Harmonics in Gases (HHG), allowing radiation down to 0.8 nm to be produced, two beam loops are foreseen to increase the beam current in using the energy recovery technique. They will accommodate fs synchrotron radiation sources in the IR, VUV and X ray ranges together with a FEL oscillator in the 10 nm range. Moreover, an important synergy is expected between accelerator and laser communities. Indeed, electron plasma acceleration will be tested and hard X ray femtosecond radiations will be produced by Thomson Scattering. The first phase of the project, ARC-EN-CIEL phase 1, is now under study. A general overview will be given.
The first applications of a storage ring Free Electron Laser started in 1993 on the Super-ACO FEL with the study of the anisotropy decay of a coenzyme, NADH, allowing to understand the thermodynamical equilibrium of the different conformational states of the molecule and their hydrodynamical volume in solution. After this first one- color experiment using the time-resolved fluorescence technique, a transient absorption experiment was developed in which the system is excited with the UV FEL and is probed by Visible-UV absorption using synchrotron radiation. First results on the dynamical behavior were obtained for the acrinide molecule.
The Super-ACO storage ring FEL is operating with a high average power in the UV range (300 mW at 350 nm), and recently at wavelengths down to 300 nm. In addition this source exhibits high stability and long lifetime which makes it a unique tool for user applications. The coupling of the FEL with other synchrotron based sources (bending magnet and undulator) opens many unexplored possibilities for various types of two-color time-resolved spectroscopies. Presently, we are developing a two-color experiment where we study the sub-nanosecond time-resolved absorption of different chromophoric compounds. In this type of pump-probe experiments, the intense UV pulse of the Super-ACO FEL is used to prepare a high initial concentration of chromophores in their first singlet electronic excited state. The nearby bending magnet synchrotron radiation provides on the other hand a pulsed, white light continuum ranging from UV to IR, which is naturally synchronized with the FEL pulses and can be used to probe the photochemical subsequent events and the transient species. With a dye molecule (POPOP), we have obtained a two-color effect which demonstrates the feasibility of the experiment in terms of flux. Applications on various chromophores of biological interest are planned.
This paper reports on the first characterization of the polarization generated by the crossed overlapped electromagnetic undulator, OPHELIE, of the new high flux/high resolution VUV beamline, SU5, in the Super-ACO storage ring at LURE. The beamline configuration for these tests was reduced after the undulator to a single mirror M1, a TGM monochromator and a multiple-reflection polarimeter. The versatility of polarizations generated by the undulator has been demonstrated around 7 eV by the measurements after the monochromator of highly polarized light either linearly (Ptot greater than 95%) or circularly (Ptot up to 80%). The standard mode of operation which produces a strong vertical linear polarization as well as the other exotic modes like the horizontal and the tilted linear polarizations, the left- and right-handed polarization and the switching between these modes, have been validated for a very large range of photon energies across the undulator spectrum.
The UV-storage ring Free Electron Laser (FEL) operating at Super-ACO is a tunable, coherent and intense (up to 300 mW) photon source in the near-UV range (300 - 350 nm). Besides, it has the unique feature to be synchronized in a one-to-one shot ratio with the Synchrotron Radiation (SR) at the high repetition rate of 8.32 MHz. This FEL + SR combination appears to be very powerful for the performance of pump- probe time-resolved and/or frequency-resolved experiments on the sub-ns and ns time-scales. In particular, there is a strong scientific case for the combination of the recently- commissioned SA5 Infra-Red Synchrotron Radiation beamline with the UV-FEL, for the performance of transient IR- absorption spectroscopy on FEL-excited samples with a Fourier-transform spectrometer coupled with a microscope allowing high spectral and spatial resolution. The principle and interest of the two-color combination altogether with the description of both the FEL and the SA5 IR beamline are presented. The first synchronization signal between the IR and the UV beams is shown. The correct spatial overlap between the UV (FEL) and the IR (SR) photon beams is demonstrated by monitoring via IR-spectro-microscopy the time evolution of a single mineral particulate (kaolinite) under UV-FEL irradiation.
Infrared microspectrometry, using a synchrotron radiation source, has been developed at Super-ACO (LURE-France). In order to accommodate for constrained horizontal (45 mrad) and vertical (18 mrad) collection angles, a particular care has been devoted to the design and making of the extraction optics, in order to achieve the highest brightness as possible, for small area illumination. Experimentally, a net gain of one hundred in Signal to Noise Ratio has been measured for an upper aperture of 3 X 3 micrometers 2. Several applications are currently underway, and some of them, related to Biomedical Science are reported in this paper.
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