magnetic endstation
Advanced Soft X-ray/EUV Beam Splitter for Time-Resolved XMCD Experiments at the transition metal L-edges
The soft X-ray/EUV beam splitter is a sophisticated optical system based on conical diffraction, specifically designed for time-resolved XMCD experiments in transmission and low-intensity conditions. This system enables the spatial resolution of the harmonic content within the Fermi FEL beam. By employing a meticulously designed grating structure, grazing incidence geometry, and customized grating coatings, it facilitates highly efficient separation of all harmonic components of the FEL beam with minimal loss of intensity and preservation of the beam profile structure.
On the left (figure below), the optical configuration of the conical diffraction grating is shown. The propagation direction of the incident field is oriented perpendicular to the grating vector. In this way, exactly symmetrized (±1)st order efficiencies near the theoretical limit are easily obtained. On the right, an image of the detector showing the traces of the separated FEL spectral components as a function of their wavelength. Displayed on the right is an image of the detector, which illustrates the traces of the separated FEL spectral components in accordance with their respective wavelengths, highlighting the effectiveness of the technique.
In the figure presented at the bottom left, the intensities of the second harmonic at 473 eV (2.62 nm) and the third harmonic at 708 eV (1.75 nm) of the second stage of FEL2 are illustrated, as measured via transmission through a NiFe permalloy sample under both positive and negative magnetic fields. The intensities are plotted with respect to the undulator phase values, and the pronounced XMCD dichroism observed in the third harmonic signal depicted in the right-side figure substantiates the elliptical degree of polarization present in the FEL pulses.
In the short video below, a series of consecutive single-shot images for positive and negative fields are shown. The FEL pulses pass through a thin permalloy film deposited on a silicon membrane. The black curve indicates the XMCD signal as a function of time after the arrival of a pump pulse.
