Abstract

The nonlinear properties of ion doped solids have been studied by different techniques, particularly solids doped with Cr⁺³ and Nd⁺³ have been much investigated due to their applications as laser materials. In these materials the nonlinearity originates from the population of dopant ion metastable state, which has a complex susceptibility different from that of ground state. The real part of nonlinear refractive index is proportional to the polarizability difference Δα between excited and ground states and the imaginary part is proportional to the absorption cross section difference Δσ between excited and ground states⁽¹⁾. Most of these solids present nonlinearity which real part is one order of magnitude greater than the imaginary one. Z-scan is nowadays the most popular technique to measure n₂ and was recently applied to ion doped solids⁽²⁾. In present work we used a time resolved Z-scan method to determine not only n₂ but also the saturation intensity I, and the spontaneous lifetime τ_o (these values can be used to calculate the ground state absorption cross section σ₁, Δα and Δσ). We should remark that although τ_o is usually easily measured by fluorescence, I_s and σ₁ are difficult to measured when you don’t know precisely the dopant ion concentration N_o or when it occupies different host sites.

© 1996 IEEE