TIME-RESOLVED Z-SCAN AND THERMAL LENS MEASUREMENTS IN ER+3 AND ND+3 DOPED FLUOROINDATE GLASSES

In rare earth ion doped solids, a resonant non-linear refractive index , n(2), appears when the laser pumps one of the ion excited states and the refractive index change is proportional to the excited state popu lation. In these solids there an usually thermal and non-thermal lensi ng effects, where the non-thermal one is due to the polarizability dif ference, Delta alpha, between excited and ground states of the ions. W e have used the time resolved Z-scan and a mode-mismatched thermal len s technique with Ar+ ion laser in Er+3 (20ZnF(2)-20SrF(2)-2NaF-16BaF(2 )-6GaF(3)-(36 - x)InF3-xErF(3), with x = 1, 2, 3 and 4 mol%) and Nd+3 (20SrF(2)-16BaF(2)-20ZnF(2)-2GdF(3)-2NaF-(40 - x)InF3-xNdF(3), with x = 0.1, 0.25, 0.5-1 mol%) doped fluoroindate glasses, In both samples w e found that the non-linear refraction is due to the thermal effect, w hile the non-thermal effect is negligible. This result indicates that in fluoride glasses Delta alpha is very small (less than 10(-26) cm(3) ). We also measured the imaginary part of the non-linear refractive in dex (n(2) '') due to absorption saturation.