The third-order nonlinear optical properties of porphyrin oligomers

Using a single beam z-scan technique with a 30 ps laser pulse at 640 and 1064 nm, the real and imaginary parts of the third-order nonlinear optical susceptibilities of porphyrin oligomers for different numbers of repetition units in solutions were measured. At a probe wavelength 640 nm, the real parts of chi((3)) (R chi((3))) of oligomers which consist of porphyrins bridged by 1,4-phenylene moiety were found to be negatively enhanced significantly compared with that of the monomer. While Re chi((3)) of the oligomers increased with increasing the porphyrin unit, the value per monomer unit remains almost constant; that is, Re chi((3)) is proportional to the number of monomer units. The oligomers in which the porphyrin rings are directly attached together at the meso position exhibited enhanced imaginary parts of chi((3)) at 640 and 1064 nm. The enhanced real part was also detected at 1064 nm. These unique properties are discussed in terms of the two photon resonance process. (C) 1997 American Institute of Physics.