The optically nonlinear dye [E-N-dodecyl-4-(2-(4-docosyloxyphenyl)ethenyl)quinolinium]+-(octadecylsulfate−)x(bromide−)1−x forms noncentrosymmetric Langmuir–Blodgett films. The second-harmonic intensity increases quadratically with the number of layers in the range investigated, i.e., as I2ω(N) = I2ω(1)′N2 for 2≤ N≤ 100, and shows long-term stability. Films of the dye are almost transparent, with an absorbance of 3 × 10−4 layer−1 at the second-harmonic wavelength, but, nonetheless, the equivalent monolayer intensity, I2ω(N)/N2, is ~30% of the resonantly enhanced signal from monolayer films of the colored hemicyanine dye reported by Girling et al. [J. Opt. Soc. Am. B 4, 950 (1987)]. The second-order susceptibility, film thickness, and chromophore tilt angle relative to the normal to the substrate are χzzz(2) = 26 pm V−1 at 1.064 μm, l = 5.0 nm layer−1, and φ 30°, respectively, for x = 0.5.
© 1998 Optical Society of America
(310.3840) Thin films : Materials and process characterization
Geoffrey J. Ashwell, Tokuhiko Handa, and Rakesh Ranjan, "Improved second-harmonic generation from homomolecular Langmuir Blodgett films of a transparent dye," J. Opt. Soc. Am. B 15, 466-470 (1998)