Quadratic enhancement of the second-harmonic intensity from alternate-layer Langmuir-Blodgett films of an optically nonlinear dye and poly(T-butyl methacrylate)

Langmuir-Blodgett films of the optically nonlinear dye are non-centrosymmet ric when the LB layers are interleaved by poly(t-butyl methacrylate). The s econd-harmonic intensity increases as I-2 omega(N) = I-2 omega(1) N-2 where N is the number of active layers, and the normalised intensity is independ ent of film thickness to more than 100 bilayers. The second-order susceptib ility and chromophore tilt angle are as follows: chi(zzz)((2)) = 60 pm V-1 at 1.064 mu m and phi = 32 degrees relative to the normal to the substrate. The susceptibility is resonantly enhanced but the absorbance at the harmon ic wavelength is only 1.5 x 10(-3) bilayer(-1).