Probing the structure of freely suspended smectic-Afilms by optical second-harmonic generation

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Abstract
Optical second-harmonic generation (SHG) was used to probe the structure of freely suspended films of 4’-n-octyl-4-cyanobiphenyl (8CB) in the smectic-A phase. The intensity of the SHG from ultrathin films with thickness varying from 2 to 10 molecular layers appeared quantized, but its behavior suggested no modifications of molecular arrangement in the layers in the presence of the two ‘‘free’’ surfaces. A macroscopic theory for the SHG from a film with stratified nonlinear susceptibility is presented and compared with the experimental observation.