FEL2 circular polarized harmonics

This method overcomes previous limitations by producing on-axis radiation with significant circular polarization at the third harmonic of the fundamental FEL wavelength, enabling precise and detailed studies of magnetic circular dichroism at the Fe L3 edge.
 
The capability to generate such specialized light pulses is a leap forward in the exploration of transition metals like Fe, Co, and Ni—elements essential for understanding the magnetic properties of materials.

This advancement not only opens new avenues for magnetic studies but also promises to enhance spectroscopic investigations across different core-hole lifetimes and edges of transition metal atoms, offering a new tool for researchers in material science, quantum computing, and beyond.

The figure illustrates the layout of the experimental setup available at the MagneDyn beamline, used for measuring the magnetic asymmetry at the L3 edge of Fe in a permalloy FeNisample. The FEL radiation impinges on a sample positioned between the magnetic pole expansions of an electromagnet capable of generating a uniform magnetic field B in the sample area, with its direction parallel to the FEL beam direction. The FEL pulses transmitted by the sample are collected by a grating arranged in a conical configuration that spatially separates the third harmonic components (red lines) and those of the fundamental of FEL2 (blue lines). The intensities of these components are measured in a single shot using a microchannel plate detector coupled with a Basler CCD camera. An example of a measurement is shown in the upper panel, where the K+-1 diffraction orders of the grating for the wavelengths of the FEL fundamental emission and the third harmonic are highlighted in blue and red boxes, respectively. The non-diffracted zero order is in the center. The lower panel displays the intensity of the zero order, the first and third harmonics after full vertical binning of the image from the upper panel