Resonant nonlinear optical studies on porphyrin derivatives

The nonlinear optical properties of three porphyrin derivatives (T3,4 BCEMPP, T4 CEMPP and TPP) doped in boric acid glass were probed using the Z-scan technique at different argon-ion laser wavelengths. The nonlinear transmission characteristics of T3,4 BCEMPP and T4 CEMPP exhibit saturable absorption at 457.9 nm and 476.5 nm while these are dominated by excited state absorption at 488.0 nm. However, in the case of TPP, the excited state absorption dominates the nonlinear characteristics except at 457.9 nm. The experimental observations are explained by using the four-level saturable absorber model. Saturation intensity, excited state absorption cross-section, light-induced changes in the absorption and the refractive index along with its sign were determined at these argon-ion laser wavelengths. Furthermore, optical limiting characteristics of these samples were studied. The observed limiting action is consistent with the Z-scan studies.