In this thesis, the nonlinear properties of dye-doped liquid crystal films measured
via Z-scan technique are presented, and we¡¦ve also compared the features of nonlinear
effect between nematic and cholesteric liquid crystals, because the purpose was to
obtain a strong nonlinear effect which is polarization independent. The nonlinear
refraction of the samples would induce self-focusing/self-defocusing effect, therefore
the Z-scan technique was utilized for the measurements in this study. The degrees of
self-focusing/self-defocusing effect can be used to calculate the optical Kerr constants n2
related to the variation of refractive indices. Moreover, this technique is
uncomplicated and powerful for nonlinear effect observations, because it only requires a
single laser beam and a simple setup to measure both nonlinear refractive indices and
nonlinear absorption coefficients.
In the first section of the study, we had investigated the nonlinear effect of
azo-dye-doped liquid crystal (ADDLC) films by Z-scan technique. Owing to the
birefringence provided by homogeneous-alignment liquid crystal films and the
absorption difference between the long axis and the short axis of the azo dye, the
self-defocusing effect in nematic phase was larger than that in isotropic state as the
polarization of incident light was parallel to the long axis of aligned liquid crystals.
While we set the incident polarization perpendicular to the long axis of liquid crystals, a
self-focusing effect was observed and the in nematic phase was found smaller than
that in isotropic state. As a result, it can be analyzed that the nonlinear effect of
homogeneous aligned ADDLC films is intensely polarization-dependent.
In the second section, in order to acquire a polarization-independent nonlinear
effect, we fabricated the azo-dye-doped cholesteric liquid crystal (ADDCLC) films
which were arranged in planar texture with the reflection bands managed to avoid the III
wavelength of incident light. We had studied the nonlinear effects in different
concentrations of the azo dye and also measured the influence of incident polarizations.
We discover that when the concentration of dyes was raised, the n2 increased as well;
the nonlinear indices were almost the same in various polarized light. The incident light
suffered an average refractive index in an ADDCLC film, and azo dye arranged in
helices resulted in identical absorption to different polarized light. In summary,
employing ADDCLCs with planar texture in nonlinear optical applications, we could
achieve not only strong nonlinear effects but also high polarization independence in
liquid crystals.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0801112-155959 |
| Date | 01 August 2012 |
| Creators | Hsu, Ming-chun |
| Contributors | Ying-Guey Fuh, Shie-Chang Jeng, Wen-Jun Zheng, Wei Lee, Tsung-Hsien Lin |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0801112-155959 |
| Rights | user_define, Copyright information available at source archive |
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