Z-SCAN STUDIES IN FLUORESCEIN-DOPED BORIC-ACID GLASS

The non-linear response of fluorescein-doped boric acid glass was prob ed using the Z-scan technique. A striking contrast was observed in its non-linear transmission characteristics at different argon-ion laser wavelengths. The non-linear transmission characteristics exhibit stron g saturation behaviour at 457.9 nm whilst at 476.5 nm and 488.0 nm the response is dominated by intense excited state absorption. The experi mental observations are explained using the four-level saturable absor ber model. The excited state absorption cross-section, saturation inte nsity, light induced absorption and refraction changes have been deter mined along with the sign of the non-linearity at various argon laser wavelengths. The optical limiting characteristics of fluorescein at 47 6.5 nm and 457.9 nm are also reported. The behaviour of the sample was in agreement with the Z-scan observations.