Discrimination between electronic and thermal contributions to the nonlinear refractive index of SrAlF5:Cr+3

In ion-doped solids there is a nonlinear refractive index n(2) that is due to the polarizability difference Delta alpha between excited and ground states, the so-called population-lens (PL) effect. In addition, the thermal-lens (TL) effect is particularly important in fluoride materials, owing to their low thermal conductivity. We performed time-resolved Z-scan and mode-mismatched TL measurements at lambda = 488 nm in SrAlF5:Cr+3 In this crystal the PL effect is faster than that of the TL, owing to its relatively short metastable lifetime (93 mu s), and therefore we could temporally discriminate between these two contributions to the nonlinear refractive index. For the PL effect we measured n(2) = (6.6 + 1.7i) x 10(-11) cm(2)/W-1 and calculated Delta alpha = 3.1 x 10(-26) cm(3) and Delta alpha = 1.7 x 10(-20) cm(2). From the TL measurements we obtained the thermal diffusivity D = 6.5 x 10(-3) cm(2)s(-1) and estimated the thermal conductivity K = 1.7 x 10(-2)W cm(-1)K(-1) and ds/dT = -8.5 x 10(-7) K-1. (C) 1999 Optical Society of America [S0740-3224(99)00203-9]. OCIS codes: 190.0190, 190.4400, 190.4870, 300.6420, 160.3380, 160.4670.