Third‐order nonlinear optical properties of phthalocyanine and fullerene

We studied the third‐order nonlinear optical properties of phthalocyanine and fullerene in solution and in thin film form through third‐harmonic generation measurement. X‐ray diffraction measurement and scanning electron microscopy observation were also conducted to investigate the relationship between nonlinear optical and structural properties of the thin film. The nonlinearities depend on the π‐conjugated length and the introduction of a central metal atom. We clarify the factors for forming suitable thin films by organic molecular beam deposition. It is shown that both the crystal structure and molecular alignment can be controlled to enhance the nonlinearities of the phthalocyanine thin film, thereby providing the maximum third‐order susceptibility of 3.0×10−10 esu. We show that nonlinearities of the thin films can be estimated experimentally from those of solutions.