Paper
30 August 2005 Distinguishing between low symmetries when determining the nonlinearity of chiral thin films
Mikael Siltanen, Stefano Cattaneo, Elina Vuorimaa, Helge Lemmetyinen, Karen E. S. Phillips, Thomas J. Katz, Martti Kauranen
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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.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Mikael Siltanen, Stefano Cattaneo, Elina Vuorimaa, Helge Lemmetyinen, Karen E. S. Phillips, Thomas J. Katz, and Martti Kauranen "Distinguishing between low symmetries when determining the nonlinearity of chiral thin films", Proc. SPIE 5935, Linear and Nonlinear Optics of Organic Materials V, 59350C (30 August 2005); https://doi.org/10.1117/12.616781
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KEYWORDS
Second-harmonic generation

Polarization

Thin films

Statistical modeling

Molecules

Signal detection

Statistical analysis

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