Coherent ultra-fast magneto-optics
Coherent ultra-fast magneto-optics.
Thèses de doctorat,
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In this work we have studied the ultra-fast interaction of photons and spins in ferromagnetic materials. At first, we have detailed the origin of magneto-optical effects and the different physical processes intervening in ultra-fast magnetization dynamics, especially in the coherent dynamics. We have used a simple model based on eight levels of the Hydrogen atom to explore two aspects of ultra-fast magneto-optical experiments: the importance of the spin-orbit interaction with the laser field appearing in the relativistic Foldy-Wouthuysen development, and the relation between the magneto-optical signal and the ultra-fast magnetization dynamics at short pump-probe delays. We have modeled two types of four-wave mixing experiments: a pump-probe configuration and a three beam setting, which enabled us to distinguish between the coherences’ and the populations’ magneto-optical response. We have shown that in our simple model, the spin-orbit interaction appearing in the Foldy-Wouthuysen development acts on the magnetization dynamics in the case of a strong Zeeman interaction. We have illustrated experimentally the two different magneto-optical dynamics for the populations and coherences in a three beam four-wave mixing experiment performed on a thin garnet film. This work announces progresses in the understanding of the coherent interaction between spins and photons in ferromagnetic materials as well as the possibility of controlling magnetization coherently on a femtosecond timescale.
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