All about DESIRS: a VUV high resolution variable polarization beamline at Soleil for dichroism and spectroscopy

DESIRS, in operation since 2008 at SOLEIL, the 3rd generation French synchrotron center, is an undulator-based beamline covering the VUV range (5-40 eV) and mainly targeting has phase samples. Its general scientific case, based upon photon excitations in the valence and inner-valence shell is five-fold . 1. High resolution spectroscopy on small molecular systems, mainly of astrophysics interest 2. Spectroscopy and fragmentation of mass-selected cations, chemical reactivity and mass spectrometry 3. Photoionization dynamics 4. Alignment, vectorial correlation and chirality 5. Excitation and relaxation in the condensed matter. In order to fulfill such a program, one needs harmonic-free, high flux, high resolution and variable polarization photons. The photon source is a 10 m-long electromagnetic fully variable polarization undulator (OPHELIE2-HU640) which high harmonics are cut-off by a gas filter-and whose polarization has been fully measured and calibrated (in the linear and circular modes) with a home-made VUV polarimeter. This pseudo white beam enters then either the high resolution Fourier-Transform Spectroscopy (FIS) branch, equipped with a windowless gas cell and a free molecular beam, for absorption experiments with an unprecedented resolving power close to 106, or the monochromator branch, with a state-of-the-art resolving power in the 105-2.105 range, for all types of spectroscopies. This latter branch is connected to the multi purpose molecular beam chamber SAPHIRS, equipped with a new electron/ion imaging coincidence spectrometer (DELlCIOUS2) allowing to perform Angle-Resolved Photoelectron Spectroscopy (PES) and ion imaging on mass-selected compounds as well as Threshold-PES and TPEPICO with sub-meV resolutions. After a short introduction to the synchrotron radiation and SOLEIL, the talk will focus of DESIRS: its scientific case, the precise description of the instrumentation developed for the beamline and its performances, including the one of the FTS spectrometer and the SAPHIRS experiment, illustrated, if time permits, by a few scientific results. (author)