Second harmonic generation from alternate-layer LB films: Quadratic enhancement with film thickness
Abstract
The second harmonic generation (SHG) from alternate-layer Langmuir-Blodgett (LB) films of stilbazolium dyes and 4,4'-dioctadecyl-3,5,3',5'-tetramethyldipyrrl-methene hydrobromide increases as I(sub 2 omega(N)) = I(sub 2 omega(1))N(sup 2) for N is greater than or equal to 2 bilayers, but the equivalent monolayer signal (I(sub 2 omega (1))) is significantly less than the intensity from LB monolayers of the corresponding dye on glass. This is attributed, in part, to the different molecular tilts and, in part, to the position of the anion which influences the charge distribution within the chromophore. For alternate-layer films of E-N-octadecyl-4-(2-(4-dimethylaminophenyl)ethenyl)pyridinium octade-cylsulphate (dye I) the second-order susceptibility and chromophore tilt angle are Chi(sup 2)(sub zzz) = 45 pm/V and phi = 30 deg respectively, whereas the methoxy congener, E-N-octadecyl-4-(2-(4-methoxyphenyl)ethenyl)pyridinium octadecysulphate (dye II), has Chi(sup 2)(sub zzz) = 11 pm/V and phi = 35 deg. The nonlinear optical properties of such films are dependent upon the compatibility of the dye and spacer.
- Publication:
-
Proceedings of the Royal Society of London Series A
- Pub Date:
- May 1994
- DOI:
- 10.1098/rspa.1994.0067
- Bibcode:
- 1994RSPSA.445..385A
- Keywords:
-
- Charge Distribution;
- Film Thickness;
- Harmonic Generations;
- Optical Properties;
- Dyes;
- Molecular Structure;
- Structural Analysis;
- Optics