Valence state manipulation of Sm³⁺ ions via a phase-shaped femtosecond laser field

The ability to manipulate the valence state conversion of rare-earth ions is crucial for their applications in color displays, optoelectronic devices, laser sources, and optical memory. The conventional femtosecond laser pulse has been shown to be a well-established tool for realizing the valence state conversion of rare-earth ions, although the valence state conversion efficiency is relatively low. Here, we first propose a femtosecond laser pulse shaping technique for improving the valence state conversion efficiency of rare-earth ions. Our experimental results demonstrate that the photoreduction efficiency from Sm³ to Sm² in Sm³ -doped sodium aluminoborate glass using a π phase step modulation can be comparable to that using a transform-limited femtosecond laser field, while the peak laser intensity is decreased by about 63%, which is very beneficial for improving the valence state conversion efficiency under the laser-induced damage threshold of the glass sample. Furthermore, we also theoretically develop a (2 1) resonance-mediated three-photon absorption model to explain the modulation of the photoreduction efficiency from Sm³ to Sm² under the π-shaped femtosecond laser field.