Laser polarization-controlled photoreduction of samarium ions in sodium aluminoborate glass

The valence state conversion of lanthanide ions induced by femtosecond laser fields has attracted considerable attention due to their potential applications in areas like high-density optical storage. However, the physical mechanisms involved in valence state conversions still remain unclear. Here, we report the first experimental study of controlling the reduction of trivalent samarium ions to divalent ones in sodium aluminoborate glass by varying the polarization status of the 800 nm femtosecond laser field. As the laser field is varied from linear to circular polarization, the reduction efficiency can be greatly decreased by about fifty percent. This polarization-dependent reduction behavior is found to directly correlate with the nonresonant two-photon 4f-4f absorption probability of the trivalent samarium ions in both experiment and theory. Multiphoton excited charge transfer between oxygen and samarium is considered to be responsible for the photoreduction. Our work demonstrates a controllable and effective way in tuning the valence state conversion efficiency and sheds light on the underlying mechanisms.