Ultrafast optical control of magnetization in ferrimagnetic garnets

Abstract

This thesis presents a detailed study of ultrafast laser-induced magnetization dynamics in thin ferrimagnetic garnet films, as well as a study of the linear and non-linear optical and magnetooptical properties of such films. The experimental techniques that have been employed include spectroscopic ellipsometry, magnetization-induced second-harmonic generation, and an all-optical pump-and-probe technique. The most important result of this work is the discovery of two ultrafast photomagnetic effects that allow for direct optical control of the magnetization in this material on the femtosecond time scale. Linearly polarized laser pulses of 100 femtoseconds duration are demonstrated to instantaneously create a long-lived modification of the magnetocrystalline anisotropy field, while circularly polarized laser pulses additionally act as strong 1 Tesla magnetic field pulses. Using these effetcs, all-optical switching of the magnetization vector within 100 femtoseconds has been demonstrated, as well as coherent optical control of the precessional magnetization dynamics.