Ultrafast nonlinear optical properties and excited state dynamics of phthalocyanine thin films

We have investigated the nonlinear optical properties, optical limiting thresholds, and figures of merits for five different phthalocyanine thin films, achieved through doping in PMMA, using the Z-scan technique at 800 nm with 2 ps laser pulses. From the open-aperture Z-scan data we established that these molecules exhibit strong two photon absorption (2PA) with the nonlinear coefficients in the range of 15-200 cm/GW. We have also estimated the sign and magnitude of real part of third order nonlinearity through the closed aperture scans. Preliminary femtosecond pump-probe data suggests that the lifetimes of excited states are in the sub-100 ps regime for all the molecules in film form. Our studies provide tangible evidence that these phthalocyanines are potential candidates for multi-photon imaging and optical limiting applications.