Faraday effect using high order harmonics for ultrafast demagnetization applications

Summary form only given. Up to recent years, synchrotron radiation facilities and free electron lasers were used as a tool for implementing magneto-x-ray spectroscopies in order to study magnetic phenomena and the properties of the magnetic materials. High order harmonic generation (HHG) arises as a new source to accomplish these studies [1], benefiting from free jitter between pump and probe beams, polychromaticity to probe various edges at the same time, and a few fs temporal resolution. Nevertheless, all the HHG-based techniques, used hitherto to evaluate magnetic dynamics, still have some drawbacks limiting clearly their potential for high level application. They require the application of elliptically polarized light (complex systems), samples with magnetic domains (only conceivable in a few materials), or specific reflection geometry of the set-up (restricting the information obtained about the sample).Here we show the demonstration of another technique using linearly polarized HHG, based on the Faraday effect in resonance introduced by a Cobalt magnetic element at 60 eV. Linearly polarized light can indeed be decomposed into two circularly polarized waves of equal amplitude but opposite helicity. The Faraday effect can be observed through a magnetized sample when an external magnetic field is applied perpendicularly to its surface. It leads to a rotation of the polarization axis of the light (difference in phase of the two waves) and to a transmitted beam with elliptical polarization (difference in absorption) [2].