J. Synchrotron Rad. 9 (2002) 270-274 [ DOI 10.1107/S0909049502007161 ]
Variable linear polarization from an X-ray undulator
A. T. Young, E. Arenholz, S. Marks, R. Schlueter, C. Steier, H. A. Padmore
Advanced Light Source, Berkeley Lab, Berkeley, CA USA 94720
A. P. Hitchcock
BIMR, McMaster University, Hamilton, ON, Canada L8S 4M1
and D. G. Castner
Dept. of Chemical Engineering, Box 351750, University of Washington, Seattle, WA 98195-1750 USA
(Received 12 Dec 2001; accepted 18 April 2002)
Synopsis: The operation of an undulator which produces linearly polarized X-rays at various angles is described. Using the new technique, linear dichroism measurements of oriented polymer films are obtained on beamline 4.0.2 at the ALS.
Abstract: A new x-ray undulator has been designed and constructed which produces linearly polarized x-rays in which the plane of polarization can be oriented to a user selectable angle, from horizontal to vertical. Based on the Apple-II elliptically polarizing undulator (EPU), the undulator rotates the angle of the linear polarization by a simple longitudinal motion of the undulator magnets. Combined with the circular and elliptical polarization capabilities of the EPU operating in the standard mode, this new undulator produces soft x-ray radiation with versatile polarization control. This paper describes the magnetic structure of the device and presents an analysis of the magnetic field with varying undulator parameters. The variable linear polarization capability is then exhibited by measuring the x ray absorption spectrum of an oriented polytetrafluoroethylene thin film. This experiment, which measures the linear dichroism of the sample at two peaks near the C 1s absorption edge, demonstrates the continuous polarization rotation capabilities of the undulator.
Keywords: undulators; variable linear polarization; linear dichroism; carbon NEXAFS.
@2002 International Union of Crystallography