Electronic and thermal contributions to the non-linear refractive index of Nd3+ ion-doped fluoride glasses

In some rare-earth ion-doped solids there is a non-linear refractive index n2 due to the polarizability difference, Δα, between excited and ground states, the so-called population lens effect. In addition to that, part of the absorbed energy is converted into heat, generating the so-called thermal lens effect. The time-resolved Z-scan technique may, in some cases, discriminate electronic (population lens) and thermal non-linearities. In this study, n2 measurements of Nd3+ doped fluoride glasses are taken. The polarizability difference, Δα, and absorption cross-section difference, Δσ, between excited (4F3/2) and ground (4I9/2) states of Nd3+ are presented. We studied different kinds of fluoride glasses (fluorozirconate, fluorindate and fluoroaluminate) and the Δαʹs obtained vary between 1 and 3×10−26 cm3.