Observation of Magnetic Helicoidal Dichroism with Extreme Ultraviolet Light Vortices

We report on the experimental evidence of magnetic helicoidal dichroism, observed in the interaction of an extreme ultraviolet vortex beam carrying orbital angular momentum with a magnetic vortex. Numerical simulations based on classical electromagnetic theory show that this dichroism is based on the interference of light modes with different orbital angular momenta, which are populated after the interaction between light and the magnetic topology. This observation gives insight into the interplay between orbital angular momentum and magnetism and sets the framework for the development of new analytical tools to investigate ultrafast magnetization dynamics.

Figure 1

(a) Schematics of the experimental setup at the DiProI beam line, showing the incoming FEL beam with planar wave front, a SZP that imparts OAM to the FEL beam, the sample placed between the poles of the electromagnet and the image of the scattered beam. (b) Scanning electron microscope image of one SZP ($\ell =+1$). (c) Far field image of the interference pattern of the corresponding OAM beam and the undiffracted, OAM-free beam, featuring a spiraling intensity pattern. (d),(e) Magnetic dots $S1$ and $S2$ with corresponding remanent magnetization after applying a pulse of saturating external field $\overrightarrow{H}$ as in (a). An opposite field reverses the curling direction $m$ of the remanent magnetization in both samples.

Figure 2

(a)–(f) Experimental dichroism (corresponding to $\mathrm{MHD}m$) for $\ell =-1,0,+1$ for MVs in dot $S1$ (top) and $S2$ (bottom). (g)–(l) Numerical simulations for the same experimental parameters. (m),(n) Same as (e),(f), with the same color scale, but with a constant magnetic field applied during the acquisition in order to homogenize sample’s magnetization; to be used as a reference. The images corresponding to (a)–(d) can be found in the Supplemental Material [48].

Figure 3

Numerical simulations with same experimental parameters of (a),(b) $\mathrm{MHD}\ell$ for different $m$ and (c),(d) $\mathrm{MHD}\ell m$ for different combinations of $\ell$ and $m$.

Figure 4

(a) Far field intensity of a beam with ${\ell }_{\mathrm{in}}=0$ reflected by a MV with $m=+1$. (b) Same as (a) when the outgoing mode ${\ell }_{\mathrm{out}}={\ell }_{\mathrm{in}}$ is suppressed. (c),(d) The same results as (a) and (b) when ${\ell }_{\mathrm{in}}=1$.