Microscopic description of the inverse Faraday effect at subpicosecond time scales

This Thesis is devoted to the microscopic study of the inverse Faraday effect at subpicosecond time scales. The inverse Faraday effect (IFE) is a magnetooptical process, which leads to the generation of magnetization by circular polarized light. Ultrafast manipulation of spin dynamics is of highly importance for the development of novel concepts of information processing and data storage. Therefore, the IFE, which provides the possibility to non-thermally and coherently induce and control magnetization dynamics at femtosecond time scales, gained much significance in recent years. However, despite its relevance for technological applications, the origin of this effect is still poorly understood. A theoretical description for the IFE induced by stationary laser light was developed in 1960’ies considering the experimental conditions available at that time. However, the laser technology moved forward dramatically in the last fifty years. Magneto-optical experiments nowadays are performed by laser pulses of several tens of femtoseconds duration, which is five orders of magnitude faster than that half century ago. This leads to principally new physics of laser induced magnetic processes, which requires novel theoretical approaches for their interpretation. It is shown here in detail that the mechanisms of magnetization changes due to the IFE triggered by ultrashort laser pulses is quite different from that by stationary excitation. A new theoretical approach based on the solution of the time-dependent Schrödinger equation is provided in this Thesis. It allows to describe magnetization time evolution triggered by circularly-polarized laser pulses at subpicosecond time scales. It is shown that the ultrafast IFE consists of two processes: the stimulated Raman scattering, which leads to the change of a system’s magnetic state, and the excitation of magnetization precession due to the deviation of the magnetic vector from its ground state. [...