| Summary: | 碩士 === 國立成功大學 === 物理學系 === 88 === Abstract
Dye-doped liquid crystals (DDLCs) have potential for uses in optical holographic storage and display owing to its large light-induced reorientation effect. It is a novel material for application in optical recording. It requires low-intensity writing beams (0.3J/cm2). The resolution can reach 103 lines/mm. The storage can preserve as long as one year, and can be repeatedly writing and erasing by heating and different polarized light.
In addition, DDLC can be used as display devices switched optically. It is different from the conventional device which is usually controlled electrically. The orientation of liquid crystal molecules can be changed by polarized light. Although the DDLC has many applications, the basic mechanism in light-induced reorientation is not clear yet.
In this thesis, we use dynamic holographic technique and polarimetric technique to study the microscopic mechanism of the dynamic holographic grating in planar nematic liquid crystal (NLC) films doped with Methyl Red (MR). The results show that the LC molecules are reoriented parallelly and orthogonally to the polarization of the pump light in different time scale. Varying the polarization in the pump and the probe beams, we observe two different phase gratings which result from different LC molecular orientation affected by MR concentration gradient and diffusion. Both the qualitative explanation and the quantitative fitting are given to account for the experimental results.
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