Third Order Nonlinear Optical Responses of Metallophthalocyanines in Films and Solutions

ABSTRACTDihydrogen, copper, platinum, and lead octakis(2-ethylhexyloxy)phthalocyanines (Pc's) were studied in polystyrene films at 532 nm and in chloroform solutions at 1064 nm by picosecond degenerate four wave mixing. Resonant χ(3) values of Pc's at 532 nm (a local minimum in the absorption spectrum) at a time coincident with the 20 psec pump pulses were as high as 104 times that of CS2 by extrapolation of the response from 1 wt % PtPc in polystyrene film to a value for pure PtPc. Delay of the probe pulse as long as 3 nsec revealed acoustic responses stronger than the fast electronic responses. The films showed the expected quadratic dependence of the instantaneous reflectivity on incident intensity only for a decade of magnitude of intensity, 100–1000 MW/cm2, with the output saturating at higher intensities. Excited state absorption at 532 nm was detected in the film samples by pulse-probe spectroscopy and was shown to be a factor in the saturation observed in the NLO signals. Nonresonant χ(3) values at 1064 nm were as high as 120 times that of CS2 from measured responses of 1 wt % chloroform solutions of Pc's. Time delay of the probe revealed both fast electronic and slower acoustic responses at 1064 nm too.