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

Abstract 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 sol–gel 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 ( Δη ) was determined to be −2.17×10 −3 .