Bruno Lagarde

DESIRS: a state‐of‐the‐art VUV beamline featuring high resolution and variable polarization for spectroscopy and dichroism at SOLEIL

DESIRS is a new undulator-based VUV beamline on the 2.75 GeV storage ring SOLEIL (France) optimized for gas-phase studies of molecular and electronic structures, reactivity and polarization-dependent photodynamics on model or actual systems encountered in the universe, atmosphere and biosphere. It is equipped with two dedicated endstations: a VUV Fourier-transform spectrometer (FTS) for ultra-high-resolution absorption spectroscopy (resolving power up to 10(6)) and an electron/ion imaging coincidence spectrometer. The photon characteristics necessary to fulfill its scientific mission are: high flux in the 5-40 eV range, high spectral purity, high resolution, and variable and well calibrated polarizations. The photon source is a 10 m-long pure electromagnetic variable-polarization undulator producing light from the very near UV up to 40 eV on the fundamental emission with tailored elliptical polarization allowing fully calibrated quasi-perfect horizontal, vertical and circular polarizations, as measured with an in situ VUV polarimeter with absolute polarization rates close to unity, to be obtained at the sample location. The optical design includes a beam waist allowing the implementation of a gas filter to suppress the undulator high harmonics. This harmonic-free radiation can be steered toward the FTS for absorption experiments, or go through a highly efficient pre-focusing optical system, based on a toroidal mirror and a reflective corrector plate similar to a Schmidt plate. The synchrotron radiation then enters a 6.65 m Eagle off-plane normal-incidence monochromator equipped with four gratings with different groove densities, from 200 to 4300 lines mm(-1), allowing the flux-to-resolution trade-off to be smoothly adjusted. The measured ultimate instrumental resolving powers are 124000 (174 µeV) around 21 eV and 250000 (54 µeV) around 13 eV, while the typical measured flux is in the 10(10)-10(11) photons s(-1) range in a 1/50000 bandwidth, and 10(12)-10(13) photons s(-1) in a 1/1000 bandwidth, which is very satisfactory although slightly below optical simulations. All of these features make DESIRS a state-of-the-art VUV beamline for spectroscopy and dichroism open to a broad scientific community.

Very high spectral resolution obtained with SU5 : A vacuum ultraviolet undulator-based beamline at Super-ACO

In this article we wish to report on the commissioning of the SU5 undulator-based beamline, whose primary scientific goal deals with high-resolution spectroscopy and photon-induced dynamics in the vacuum ultraviolet range on dilute species. In order to achieve such a scientific program, we have conceived an original optical design, centered around a 6.65 m off-plane Eagle monochromator equipped with two gratings (2400 and 4300 l/mm) illuminated by an astigmatic prefocusing optical system. The different components of the actual beamline, such as the optical elements, their holders/manipulators and the monochromator are described, with a special emphasis on critical aspects such as the mechanical resolution and stability, the vibrations limitations, and the thermal stability. Then, a spectral calibration procedure of the monochromator is described, followed by the presentation of the measured performances of the beamline in terms of ultimate resolution and flux. Owing to a gas phase ion yield experiment on rare gases, we have been able to measure a raw linewidth of 184 µeV at 21.61 eV (18s line of Ne) corresponding to a resolving power of 117 000 and a raw (respectively, lifetime-deconvoluted) linewidth of 119 µeV (respectively, 76 µeV) at 15.82 eV (13s line of Ar) corresponding to a raw resolving power of 133 000 (respectively, 208 000). The ultimate targeted 105 resolving power is therefore observed on most of the VUV range, which corresponds to an unprecedented performance. The measured photon flux in a 1/50 000 bandwidth is in reasonable agreement with the expected values lying in the 1010–109 photon/s range over the VUV range. These very satisfactory performances, with a slit-limited resolution down to about 15 µm slits aperture, are due to the special care which has been paid at both the conception and construction stages concerning critical issues such as the optical and mechanical design, the vibrations, the driving/encoding system, and the slope errors of the gratings.

Synchrotron UV Fluorescence Microscopy Uncovers New Probes in Cells and Tissues

Use of deep ultraviolet (DUV, below 350 nm) fluorescence opens up new possibilities in biology because it does not need external specific probes or labeling but instead allows use of the intrinsic fluorescence that exists for many biomolecules when excited in this wavelength range. Indeed, observation of label free biomolecules or active drugs ensures that the label will not modify the biolocalization or any of its properties. In the past, it has not been easy to accomplish DUV fluorescence imaging due to limited sources and to microscope optics. Two worlds were coexisting: the spectrofluorometric measurements with full spectrum information with DUV excitation, which lacked high-resolution localization, and the microscopic world with very good spatial resolution but poor spectral resolution for which the wavelength range was limited to 350 nm. To combine the advantages of both worlds, we have developed a DUV fluorescence microscope for cell biology coupled to a synchrotron beamline, providing fine tunable excitation from 180 to 600 nm and full spectrum acquired on each point of the image, to study DUV excited fluorescence emitted from nanovolumes directly inside live cells or tissue biopsies.

ANTARES, a scanning photoemission microscopy beamline at SOLEIL

As one of the latest beamline built at the SOLEIL synchrotron source, ANTARES beamline offers a spectroscopic non-destructive nano-probe to study advanced materials. This innovative scanning photoemission microscopy combines linear and angle sweeps to perform precise electronic band structure determination by Nano Angle Resolved Photoelectron Spectroscopy (nanoARPES) and chemical imaging by core level detection. The beamline integrates effectively insertion devices and a high transmission beamline optics. This photon source has been combined with an advanced microscope, which has precise sample handling abilities. Moreover, it is fully compatible with a high resolution R4000 Scienta hemispherical analyzer and a set of Fresnel Zone Plates (FZP) able to focalize the beam spot up to a few tenths of nanometers, depending on the spatial resolution of the selected FZP. We present here the main conceptual design of the beamline and endstation, together with some of the firsts commissioning results.

Design and performance of AERHA, a high acceptance high resolution soft x-ray spectrometer

A soft x-ray spectrometer based on the use of an elliptical focusing mirror and a plane varied line spacing grating is described. It achieves both high resolution and high overall efficiency while remaining relatively compact. The instrument is dedicated to resonant inelastic x-ray scattering studies. We set out how this optical arrangement was judged best able to guarantee performance for the 50 - 1000 eV range within achievable fabrication targets. The AERHA (adjustable energy resolution high acceptance) spectrometer operates with an effective angular acceptance between 100 and 250 μsr (energy dependent) and a resolving power well in excess of 5000 according to the Rayleigh criterion. The high angular acceptance is obtained by means of a collecting pre-mirror. Three scattering geometries are available to enable momentum dependent measurements with 135°, 90°, and 50° scattering angles. The instrument operates on the Synchrotron SOLEIL SEXTANTS beamline which serves as a high photon flux 2 × 200 μm(2) focal spot source with full polarization control.

The SEXTANTS beamline at SOLEIL: a new facility for elastic, inelastic and coherent scattering of soft X-rays

SEXTANTS is a new SOLEIL beamline dedicated to soft X-ray scattering techniques. The beamline, covering the 50-1700 eV energy range, features two Apple-II undulators for polarization control and a fixed-deviation monochromator. Two branch-lines host three end-stations for elastic, inelastic and coherent scattering experiments.

DISCO synchrotron‐radiation circular‐dichroism endstation at SOLEIL

The new synchrotron-radiation circular-dichroism (SRCD) endstation on the UV-visible synchrotron beamline DISCO has been commissioned at the SOLEIL synchrotron. The design has been focused on preservation of a high degree of linear polarization at high flux and moderate resolving power covering the vacuum ultraviolet to visible spectral range (125-600 nm). The beam dimensions have been set to 4 mm × 4 mm at 1 nm bandwidth for lower sample degradation. The nitrogen-purged sample chamber fits three types of sample holders accommodating conventional round cell mounting, automated rotation of the samples, as well as a microfluidic set-up. Automated temperature-controlled data collection on microvolumes is now available to the biology and chemistry communities. Macromolecules including membrane proteins, soluble proteins, bio-nanotubes, sugars, DNA and RNAs are now routinely investigated.

Carbon contamination of soft X-ray beamlines: dramatic anti-reflection coating effects observed in the 1 keV photon energy region.

Carbon contamination is a general problem of under-vacuum optics submitted to high fluence. In soft X-ray beamlines carbon deposit on optics is known to absorb and scatter radiation close to the C K-edge (280 eV), forbidding effective measurements in this spectral region. Here the observation of strong reflectivity losses is reported related to carbon deposition at much higher energies around 1000 eV, where carbon absorptivity is small. It is shown that the observed effect can be modelled as a destructive interference from a homogeneous carbon thin film.

A NEW VUV HIGH RESOLUTION UNDULATOR-BASED BEAMLINE AT SUPER-ACO

Abstract The VUV undulator-based high resolution SU5 beamline, designed to operate in the 5–45 eV photon energy range, is under construction at Super-ACO. It is composed of three toroidal mirrors around a 6.65 m Eagle off-plane normal incidence monochromator, whose induced-astigmatism is negligible owing to an horizontal focusing onto the gratings. With an optical design minimizing the aberrations and optimizing the throughput through the entrance slit, and with a careful choice of the optical coatings, the SU5 beamline should provide in the near future more than 1010 ph/s at the sample level for a 1 50 000 bandwidth in the 5–25 eV energy range. The ultimate resolving power should be higher than 105.

A differential pumping system to deliver windowless VUV photons at atmospheric pressure.

In order to deliver VUV (vacuum ultraviolet) photons under atmospheric pressure conditions, a differential pumping system has been built on the DISCO beamline at the SOLEIL synchrotron radiation facility. The system is made of four stages and is 840 mm long. The conductance-limiting body has been designed to allow practicable optical alignment. VUV transmission of the system was tested under air, nitrogen, argon and neon, and photons could be delivered down to 60 nm (20 eV).