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 χ(3)(−3ω; ω, ω, ω) 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 χ(3) value of the film grown epitaxially on KBr was 2.87×10−10 esu, which was greater by a factor of about 7.7 than that of a polycrystalline film grown on fused silica. The enhancement of χ(3) in the epitaxial phase is associated with the optimized orientation of the two-dimensional π-electron system in the condensed phase.