Speaker
Description
Optical probing of magnetization dynamics has traditionally relied on analyzing the polarization of plain Gaussian beams. Recently, we introduced a novel approach – Magnetic Helicoidal Dichroism (MHD) – based on analyzing the reflectivity of beams with twisted wavefronts, i.e., beams carrying orbital angular momentum.
While the spin angular momentum of light is widely used in dichroic studies — such as X-ray magnetic circular dichroism or Magneto-Optical Kerr Effect — the orbital angular momentum (OAM) degree of freedom has been far less explored. Recently, some of us demonstrated that OAM can enhance ptychographic XUV imaging resolution. Besides, by controlling the sign of the incoming OAM, we also showed that it can reveal the orientation of magnetic textures, such as the curling sense of a magnetic vortex, an effect termed Magnetic Helicoidal Dichroism.
Recently, we leveraged this technique to track the ultrafast dynamics of an oriented inhomogeneous magnetic texture. In particular, we identified a transient inversion of the curling sense of a magnetic vortex during its recovery following partial demagnetization initiated by a femtosecond laser pulse. A key advantage of Time-Resolved MHD is its ability to operate without a real space imaging of the spin texture, enabling rapid measurements of a meaningful parameter with just a few intensity patterns. These results hold great promise not only for monitoring the dynamics of complex magnetic textures but also for uncovering new forms of magnetic optical spin-orbit interactions.