How do spins interact coherently with ultrashort laser pulses ?

TL;DR

This paper models the coherent interaction between ultrashort laser pulses and spins, revealing the mechanisms behind ultrafast magnetization dynamics and clarifying recent experimental controversies.

Contribution

It provides a theoretical framework including relativistic effects for understanding femtosecond laser-spin interactions in ferromagnets.

Findings

Explains the origin of coherent magneto-optical responses.

Identifies roles of spin-photon interaction and spin dynamics.

Supports recent experimental observations in ferromagnetic thin films.

Abstract

We investigate the interaction of femtosecond laser pulses with spins including relativistic corrections. The time-ordered magneto-optical signals corresponding to a pump-probe configuration are calculated in the case of one electron submitted to a magnetic field and evolving in eight levels of the fine structure of a hydrogen-like atom. Our simulations explain the origin of the coherent magneto-optical response and ultrafast spin dynamics in ferromagnets excited by intense laser pulses as recently reported in Ni and CoPt3 ferromagnetic thin films. Our detailed analysis allows identifying the respective roles of the coherent spin-photon interaction and spin dynamics unraveling recent controversies about the laser induced ultrafast magnetization dynamics.