Abstract
X-ray circular dichroism (XMCD), one of the main tools to study magnetism, benefits enormously from the capability of a fast alterable helicity of circularly polarized X-ray photons. Here we present a method for boosting the alternating frequency between right- and left-handed photons to the MHz regime, more than three orders of magnitude faster than state-of-the-art technologies. The method is based on a twin elliptical undulator installed in an electron storage ring being operated in a novel mode where the electron optics is tuned close to a resonance with electrons captured in transverse resonance island buckets. Propagating through the twin undulator, electrons from different islands emit photons of the same wavelength but of opposite helicity. These two helicity components can be alternated as fast as 2 ns. In a proof-of-principle experiment at BESSY II, we demonstrate XMCD at the L2,3 absorption edges of Ni with an 800 ns helicity flip.
Highlights
X-ray circular dichroism (XMCD), one of the main tools to study magnetism, benefits enormously from the capability of a fast alterable helicity of circularly polarized X-ray photons
As the slow processes determine the time needed for the experiment, typically two energy-dependent spectra are recorded subsequently with a helicity or magnetization change in between. This scheme is acceptable when sample and all other experimental parameters are stable over the whole time of the experiment, studies from dynamical processes and experiments addressing small effects such as in molecular spin systems on surfaces, spatially resolved magnetic domains, and quasi-particles in solids[12] significantly benefit from a scheme where very fast helicity alternation in the MHz regime allows for a quasisimultaneous acquisition of both X-ray helicities such that the XMCD spectrum can be recorded in a single energy sweep
Diffraction-limited light sources with round beams, small divergence, and small magnetic gaps will help in this aspect
Summary
X-ray circular dichroism (XMCD), one of the main tools to study magnetism, benefits enormously from the capability of a fast alterable helicity of circularly polarized X-ray photons. As the slow processes determine the time needed for the experiment, typically two energy-dependent spectra are recorded subsequently with a helicity or magnetization change in between This scheme is acceptable when sample and all other experimental parameters are stable over the whole time of the experiment, studies from dynamical processes and experiments addressing small effects such as in molecular spin systems on surfaces, spatially resolved magnetic domains, and quasi-particles in solids[12] significantly benefit from a scheme where very fast helicity alternation in the MHz regime allows for a quasisimultaneous acquisition of both X-ray helicities such that the XMCD spectrum can be recorded in a single energy sweep. They need a small intermediate focus (not standard at soft X-ray beamlines), a gap in the storage ring filling pattern, which is not foreseen in most low-emittance machines of the generation and—in the specific case mentioned above—a special double slit geometry to switch between two separated beams
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
