Z-scan measurements of the nonlinear absorption and refractive index for fluorescein 548-doped organically modified sol-gel silica films

Free-standing poly(acrilic acid) modified sol-gel silica thick films doped with fluorescein 548-doped were prepared. The nonlinearity of the refractive index and absorption of the films were studied by the Z-scan technique. Strong absorption nonlinearity was observed in the sot-get samples when pumped by a CW argon ion laser at both 457.9 and 476.5 nm. Experimental results were interpreted with a four-level model. Saturation intensity and triplet-state absorption coefficient at these wavelengths were determined by curve fitting. Refractive nonlinearity was also observed at 457.9 nm. The intensity induced change of the refractive index (Delta eta) was determined to be -2.17 x 10(-3). (C) 2001 Elsevier Science B.V. All rights reserved.