Enhancement of the third-order nonlinear optical susceptibility in epitaxial vanadyl-phthalocyanine films grown on KBr

We determined the magnitude of the third-order nonlinear optical susceptibilities chi((3))(-3 omega; omega, omega, omega) of vanadyl-phthalocyanine (VOPc) films grown on KBr and fused silica substrates, using the third harmonic generation method at a wavelength of 1200 nm. The chi((3)) value of the him grown epitaxially on KBr was 2.87 x 10(-10) esu, which was greater by a factor of about 7.7 than that of a polycrystalline film grown on fused silica. The enhancement of chi((3)) in the epitaxial phase is associated with the optimized orientation of the two-dimensional pi-electron system in the condensed phase. (C) 1996 American Institute of Physics.