## Abstract

In ion-doped solids there is a nonlinear refractive index ${n}_{2}$ that is due to the polarizability difference Δ*α* 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 $\mathrm{\lambda}=488\mathrm{nm}$ in ${\mathrm{SrAlF}}_{5}:{\mathrm{Cr}}^{+3}.$ In this crystal the PL effect is faster than that of the TL, owing to its relatively short metastable lifetime (93 *µ*s), and therefore we could temporally discriminate between these two contributions to the nonlinear refractive index. For the PL effect we measured ${n}_{2}=(6.6+1.7i)\times {10}^{-11}{\mathrm{cm}}^{2}/{\mathrm{W}}^{-1}$ and calculated $\mathrm{\Delta}\alpha =3.1\times {10}^{-26}{\mathrm{cm}}^{3}$ and $\mathrm{\Delta}\sigma =1.7\times {10}^{-20}{\mathrm{cm}}^{2}.$ From the TL measurements we obtained the thermal diffusivity $D=6.5\times {10}^{-3}{\mathrm{cm}}^{2}{\mathrm{s}}^{-1}$ and estimated the thermal conductivity $K=1.7\times {10}^{-2}\mathrm{W}{\mathrm{cm}}^{-1}{\mathrm{K}}^{-1}$ and $\mathrm{d}s/\mathrm{d}T=-8.5\times {10}^{-7}{\mathrm{K}}^{-1}.$

© 1999 Optical Society of America

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