The optically nonlinear dye [E-N-dodecyl-4-(2-(4-docosyloxyphenyl)ethenyl)quinolinium]<sup>+</sup>-(octadecylsulfate<sup>−</sup>)<sub>x</sub>(bromide<sup>−</sup>)<sub>1−x</sub> forms noncentrosymmetric Langmuir–Blodgett films. The second-harmonic intensity increases quadratically with the number of layers in the range investigated, i.e., as <i>I</i><sub>2ω(N)</sub> = <i>I</i><sub>2ω(1)</sub><sup>′</sup><i>N</i><sup>2</sup> for 2≤ N≤ 100, and shows long-term stability. Films of the dye are almost transparent, with an absorbance of 3 × 10<sup>−4</sup> layer<sup>−1</sup> at the second-harmonic wavelength, but, nonetheless, the equivalent monolayer intensity, <i>I</i><sub>2ω(N)</sub>/<i>N</i><sup>2</sup>, 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 <b>4</b>, 950 (1987)]. The second-order susceptibility, film thickness, and chromophore tilt angle relative to the normal to the substrate are χ<sub>zzz</sub><sup>(2)</sup> = 26 pm V<sup>−1</sup> at 1.064 μm, <i>l</i> = 5.0 nm layer<sup>−1</sup>, and φ 30°, respectively, for <i>x</i> = 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)