Bulk and surface contributions to the second-harmonic generation in tetra-aminodiphenyl films

The second-harmonic generation in thin (from 430 to 2330 nm) tetra-aminodiphenyl films obtained by thermal evaporation in vacuum is investigated. The dependences of the quadratic optical susceptibility on the film thickness are analyzed for several models assuming different location of nonlinear sources. The film nonlinearity is shown to have a bulk character.