Improved Second-Harmonic Generation from Langmuir−Blodgett Films

Abstract

The second-harmonic intensity from alternate-layer Langmuir−Blodgett films of a coumarin dye, 4-[2-(7-diethylamino-2-oxo-2H-benzopyran-3-yl)ethenyl]-1-octadecylquinolinium bromide, and an inert spacer, 1-octadecyl-4-methylquinolinium bromide, increases quadratically with the number of active layers. The optimum effective second-order susceptibility, albeit resonantly enhanced, is the highest to date for a thick alternate-layer film with χeff(2) = 190 ± 30 pm V-1 at 1.064 μm. The thickness and the real and imaginary components of the dielectric permittivity from the surface plasmon resonance at 532 nm are l = 4.6 ± 0.4 nm bilayer-1, εr = 2.4 ± 0.2 and εi = 0.8 ± 0.2.