magnetic endstation

The WollasTON polarImeter for X-ray FEL sources (TONIX), is an energy-tunable polarimeter specifically designed for ultrashort linearly polarized extreme ultraviolet (EUV) pulsed sources and pump-probe experiments. Featuring high detection efficiency, it enables single-shot determination of the X-ray polarization angle for both diagnostic and spectroscopic investigations. Integrated directly into the beam path or by capturing a portion of the beam, the TONIX provides real-time measurement of the linear polarization angle. This angle can be altered by various physical phenomena, including magnetic order, high-density plasma matter, impurity domains, and strain. As a result, the TONIX can detect significant contrast in situations where intensity-based detection devices may not discern any noticeable differences. A simple algorithm returns the polarization angle of the detected beam for each single pulse. it is currently installed at the MagneDyn beamline at FERMI FEL and is available for researchers to utilize.  Brief description of its operating principle: The incoming FEL beam (depicted in green) is divided by the first mirror, at the Brewster angle, which reflects the radiation onto the multi-channel plate (MCP) detector, MCP-R. The transmitted beam is then reflected by the second mirror, onto MCP-T.   A. Caretta et al., Structural Dynamics 8, 034304 (2021)

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.