Nanospectroscopy Beamline Description

Insertion device

The Nanospectroscopy beamline shares the insertion device with the Elettra Free Electron Laser (EuFEL). Based on the Sasaki Apple II scheme, the photon source consists of two identical undulator sections (each with 20 poles and period 10 cm) and a phase modulation electromagnet arranged in an optical klystron configuration. Documentation is provided here (EPAC_2216.pdf; EPAC_2322.pdf; EPAC_2349.pdf). 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 below 40 eV to 1000 eV, with high brilliance (using the first, third and fifth undulator harmonics). We emphasize 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.