Quadratic Enhancement of the Second-Harmonic Intensity from Alternate-Layer Langmuir-Blodgett Films of an Optically Nonlinear Dye and Poly(T-Butyl Methacrylate)

Abstract

Langmuir-Blodgett films of the optically nonlinear dye are non-centrosymmetric when the LB layers are interleaved by poly(t-butyl methacrylate). The second-harmonic intensity increases as I2ω(N) = I2ω(1) N2 where N is the number of active layers, and the normalised intensity is independent of film thickness to more than 100 bilayers. The second-order susceptibility and chromophore tilt angle are as follows: χ(2) zzz = 60 pm V−1 at 1.064 μm and φ = 32° relative to the normal to the substrate. The susceptibility is resonantly enhanced but the absorbance at the harmonic wavelength is only 1.5 × 10−3 bilayer−1.