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 n(2) due to the polarizability difference, Delta alpha, 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, n(2) measurements of Nd3+ doped fluoride glasses are taken. The polarizability difference, Delta alpha, and absorption cross-section difference, Delta sigma, between excited (F-4(3/2)) and ground (I-4(9/2)) states of Nd3+ are presented. We studied different kinds of fluoride glasses (fluorozirconate, fluorindate and fluoroaluminate) and the Delta alpha s obtained vary between 1 and 3 x 10(-26) cm(3). (C) 2000 Elsevier Science B.V. All rights reserved.