Discrimination of Resonant and Nonresonant Contributions to the Nonlinear Refraction Spectroscopy of Ion-Doped Solids

Nonlinear refraction spectroscopy measurements were performed in resonance with absorption lines in Nd 3+ and Cr 3+ doped crystals. The observed line shapes can be explained by the interference of resonant and nonresonant contributions to the nonlinear refractive index. These effects were fully discriminated using a pump and probe configuration, in which a dispersive line shape was observed on the top of a plateau that was attributed to the polarizability difference between excited and ground states (A a). A theoretical model was used to obtain A a from the experimental data, and the results are in agreement with several previous experiments. Slow and fast light propagation are also discussed.