Nuclear Instruments and Methods in Physics Research A 467–468 (2001) 453–457 Complete characterization of SU5: a VUV high resolution beamline with variable polarizations L. Nahon a,b, *, F. Polack a , B. Lagarde a , R. Thissen c , C. Alcaraz a , O. Dutuit a,c , K. Ito d a LURE, Bat 209D, Universit ! e Paris-Sud, BP 34, 91898 Orsay Cedex, France b DRECAM/SPAM, Bat 522, CE de Saclay, 91191 Gif sur Yvette Cedex, France c LCP, Bat 350, Universit ! e Paris-Sud, 91405 Orsay Cedex, France d Photon Factory, KEK, Tsukuba 305, Japan Abstract The SU5 VUV beamline aims towards a dual scientific program: high resolution spectroscopy on dilute targets and linear/circular dichroism on anisotropic systems. A crossed planar/helicoidal electromagnetic undulator has been designed and built, providing both flux and variable polarizations. We have shown a complete versatility of the polarization state of the emitted light with high polarization rates. Besides, the harmonics of the undulator can be suppressed owing to a gas filter, acting as a low-energy pass filter, with rejection factors above 10 5 . The beamline is centered around a 6.65 m off-plane Eagle normal incidence monochromator which has shown unprecedented raw resolving powers (117 000 at 21.6 eV, 133 000 at 15.8 eV) with typical flux in a 1/50 000 bandwidth of 10 10 –10 9 photons/s between 6 and 30 eV. # 2001 Elsevier Science B.V. All rights reserved. PACS: 07.60.Rd; 41.60.Ap; 42.15.Eq; 42.25.Ja Keywords: Synchrotron radiation; Insertion device; Polarization; VUV spectroscopy; Monochromator; High resolution 1. Introduction The new SU5 beamline at Super-ACO (see also Ref. [1]) is primarily devoted to the study, in the VUV range, of very high resolution spectroscopy and photon-induced dynamics on diluted species. A second scientific case deals with the study of anisotropic systems via linear and circular dichro- ism experiments, requiring the use of ‘‘exotic polarizations’’, i.e. rotating linear and circular polarizations. To our knowledge, this is the only VUV beamline which aims towards both high resolution and dichroism capabilities. Other beam- lines such as the planar undulator-based Chemical Dynamics Beamline (CDF) at the Advanced Light Source (ALS) [2,3] have obtained high resolution with monochromators (70000 resolving power) and high flux, while some others have used fixed- grating spectrometers to perform ultra-high resolution (250000 resolving power) absorption spectroscopy [4]. On the other hand, the only VUV *Corresponding author. LURE, Bat 209D, Universite Paris- Sud, Batiment 209D, BP 34, F-91898 Orsay Cedex, France. Tel.: +33-1-64-46-88-60; fax: +33-1-64-46-41-48. E-mail address: nahon@lure.u-psud.fr (L. Nahon). 0168-9002/01/$-see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0168-9002(01)00356-4