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Proceedings Paper

Distinguishing between low symmetries when determining the nonlinearity of chiral thin films
Author(s): Mikael Siltanen; Stefano Cattaneo; Elina Vuorimaa; Helge Lemmetyinen; Karen E. S. Phillips; Thomas J. Katz; Martti Kauranen
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Paper Abstract

New nonlinear organic materials are conveniently studied and characterized as thin film samples. The macroscopic nonlinear response described by the susceptibility tensor is closely related to the quality of the sample, ordering of molecules, and other properties of the film. In order to characterize the nonlinearity properly and to access the resulting information, the susceptibility tensor should be accurately determined. Unfortunately, this requires a theoretical model of the nonlinear interaction, where certain assumptions, whose validity is often difficult to verify, must be made. This may compromise the reliability of the results. We use a technique based on the polarization properties of second-harmonic generation to characterize thin films, which facilitates the verification of the assumptions while allowing the determination of the susceptibility tensor. Chiral molecules have no center of symmetry and are therefore naturally very interesting subjects of study in secondorder nonlinear optics. We apply our technique to chiral, anisotropic Langmuir-Blodgett films of helicene molecules to obtain the relative values of the components of their susceptibility tensors and estimates of their accuracy. Usually such samples are assumed to have C2 symmetry, but we prepare samples having different structures and report results where the symmetry groups C2 and D2 can be distinguished. In addition, the orientation of the in-plane symmetry axis that appears in D2 but is absent in C2 is determined.

Paper Details

Date Published: 30 August 2005
PDF: 9 pages
Proc. SPIE 5935, Linear and Nonlinear Optics of Organic Materials V, 59350C (30 August 2005); doi: 10.1117/12.616781
Show Author Affiliations
Mikael Siltanen, Tampere Univ. of Technology (Finland)
Stefano Cattaneo, Tampere Univ. of Technology (Finland)
Elina Vuorimaa, Tampere Univ. of Technology (Finland)
Helge Lemmetyinen, Tampere Univ. of Technology (Finland)
Karen E. S. Phillips, Columbia Univ. (United States)
Thomas J. Katz, Columbia Univ. (United States)
Martti Kauranen, Tampere Univ. of Technology (Finland)

Published in SPIE Proceedings Vol. 5935:
Linear and Nonlinear Optics of Organic Materials V
Manfred Eich, Editor(s)

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