Light induced magnetization in a spin S=1 easy - plane antiferromagnetic chain

The time evolution of magnetization induced by circularly polarized light in a $S=1$ Heisenberg chain with large, easy--plane anisotropy is studied numerically and analytically. Results at constant light frequency $\Omega=\Omega_0$ are interpreted in terms of absorption lines of the electronic spin resonance spectrum. Applying a time dependent light frequency $\Omega=\Omega(t)$, so called chirping, is shown to be an efficient procedure in order to obtain within a short time a large, controlled value of the magnetization $M^z$. Furthermore, comparison with a $2$ - level model provides a qualitative understanding of the induced magnetization process.