All-optical switching characteristics of metalloporphyrins

We present all-optical switching in Zinc (II) tetraphenylporphyrin (ZnTPP) and Vanadium (IV)-oxide tetraphenylporphyrin (VOTPP) using pump probe method. A cw probe laser beam of 633 nm passing through the dye solutions is switched by a 20-ns pulsed pump laser beam of 532 nm. Our results show that there is an optimum value of concentration of the medium for which maximum modulation of the probe beam can be achieved. Probe beam modulation saturates after a certain value of pump intensity. Switch 'off' and 'on' time for VOTPP are ∼1.5 and ∼2.5 μs, respectively and for ZnTPP, respective times are ∼200 ns and ∼3.5 μs. Experimental results have been explained by doing a theoretical analysis based on nonlinear intensity induced excited state absorption using the rate equation model. Our analysis indicates that in VOTPP the long switch off time could be due to the existence of an intermediate state between the first singlet and triplet state.