| Summary: | 碩士 === 國立成功大學 === 物理學系 === 88 === In this thesis, we study the dynamic behavior of the photorefractive effect on Dye Doped Liquid Crystal (DDLC) films. The two pump beams derived from a Krypton Ion Laser (l=568.4nm) set up a periodic interference of light on the DDLC sample, generating a phase grating. From the dynamic first order diffraction intensity of the probe beam (He-Ne Laser, l=632.8nm), we believe that the photoexcited dye molecules are diffusing slowly and then adsorbing onto the inner surfaces. These dye molecules induce a negative reorientational nonlinearity to the liquid crystal molecules in the high-intensity regions of interference patterns. After suitable illumination time, the photographs (SEM and AFM) show that the Methyl Red molecules adsorb onto the surfaces and form laser-induced ripple structures. These photoexcited dye molecules exert an intermolecular torque inducing transient dynamic sliding followed by permanent reorientation. Under an application of an external voltage, the space charge field effect and the intermolecular torque are competing each other. Finally, the strong negative nonlinearity induces a permanent grating. We can switch off the grating by applying an external voltage. The study of the application for optical data storage is underway.
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