PADReS description copy

Overview

In order to to achieve high spatial resolution and maximize collection efficiency, the beamline was designed to convey the highest possible flux density at the microscope focus. Target requirements were met by combining an insertion device with a moderate energy resolving power monochromator, together with micro spot refocusing of the photon beam. Given the typical working conditions of the microscope (2 μm to 5 μm field of view), the beamline strongly demagnifies the source, providing homogeneous illumination of the sample area which is imaged by the microscope.

Insertion device

The Nanospectroscopy beamline shares the insertion device with the Elettra Free Electron Laser (EuFEL). Based on the Sasaki Apple II scheme, it consists of two identical undulator sections (Elettra insertion devices 1.1 and 1.2) and a phase modulation electromagnet arranged in an optical klystron configuration. This enables the two undulators to be properly phased, thus effectively doubling the undulator length and the useful flux. During the storage ring FEL operation, this configuration offers the benefit of an increased laser gain. The insertion device is able to provide elliptically polarized light (circular left and right as well as linear horizontal and vertical as special cases) in a spectral range extending from 50 eV to 1000 eV, with high brilliance (using the first, third and fifth undulator harmonic). We emphasis the undulator capability of helicity inversion, which allows performing XMCD (X-Ray Magnetic Circular Dichroism) measurements. The optimum phase for measurements requiring circular polarisation can be found here.

Beamline Layout

The light source is the middle-point (4) between the undulator two sections (1) and (2) with phase modulator electromagnet (3).At 10 m from the source middle position, the pinhole (5) sets the beamline angular acceptance and stops unwanted radiation from the undulator.The toroidal mirror (6) demagnifies the source by a factor of 8 in the horizontal plane and 5.3 in the vertical. The entrance slits are located at the horizontal (7) and vertical (8) foci of the toroidal mirror. The slit (7) becomes the virtual source for all of the following mirrors in the horizontal plane. The light is then dispersed by the monochromator (9),which also determines a further vertical demagnification by a factor 1.7. After the exit-slit (10), a retractable plane mirror (11) allows switching operation between the two branches of the beamline. The refocusing mirrors are two bendable elliptical cylinder mirrors arranged in a Kirkpatrick-Baez geometry. They are located in dedicated vacuum chambers (12). On the beamline first branch, the demagnification introduced by these elements is 11.5 in the horizontal direction and 5 in the vertical direction. For the second branch, the demagnification factors are 13.9 and 7.6, for the horizontal and the vertical direction respectively.{/multicols}