title: Investigation of the polarization state of dual APPLE-II undulators.
abstract: The use of an APPLE II undulator is extremely important for providing a high-brilliance X-ray beam with the capability to switch between various photon beam polarization states. A high-precision soft X-ray polarimeter has been used to systematically investigate the polarization characteristics of the two helical APPLE II undulators installed on beamline I06 at Diamond Light Source. A simple data acquisition and processing procedure has been developed to determine the Stokes polarization parameters for light polarized at arbitrary linear angles emitted from a single undulator, and for circularly polarized light emitted from both undulators in conjunction with a single-period undulator phasing unit. The purity of linear polarization is found to deteriorate as the polarization angle moves away from the horizontal and vertical modes. Importantly, a negative correlation between the degree of circular polarization and the photon flux has been found when the phasing unit is used.
authors.affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Hand
authors.affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, UK.
authors.forename: Hongchang
authors.initials: H
authors.lastname: Wang
authors.affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, UK.
authors.forename: Sarnjeet S
authors.initials: SS
authors.lastname: Dhesi
authors.affiliation: Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, UK.
authors.forename: Kawal
authors.initials: K
authors.lastname: Sawhney
keywords: multilayers; polarization; undulators