| Summary: | 碩士 === 國立成功大學 === 光電科學與工程研究所 === 98 === This thesis investigates electrically, thermally, and all-optically controllable random lasers based on dye-doped liquid crystal (DDLC) films with BaTiO3 nanoparticles. Experiment result show that the random lasing emission is resulted from the multiple-scattering of the nanoparticles in LC host and can be electrically, thermally and all-optically controlled by varying the applied voltage, the cell temperature, and the exposure times of one UV and one green beams, respectively. The mechanisms of the three controllabilities of the random lasers are described as follows:
(1) The orientational changes of the LCs from homogeneous to homeotropic texture in the presence of increasing applied voltage lead to the absorption and thus the fluorensence emission of the laser dyes to decrease, resulting in the decrease of the random lasing emission.
(2) The increasing destructive scattering resulting from the increasing fluctuation of LCs at increasing temperature can decrease the multiple-scattering effect of the nanoparticles in LCs host, resulting in the decrease of the random lasing. A strong random lasing emission can reappear once the LC-fluctuation-induced destructive scattering is disappeared as the LCs becomes isotropic.
(3) All-optical controllability of the random lasing can be obtained by successively irradiating one UV and one green beam on the azo-dye-added DDLC with nanoparticles.The exposure of the UV (green) beam can cause the increase (decrease) of the LC-fluctuation-induced destructive scattering due to the trans→cis (cis-trans back) isomerization of the azo dyes. This may induce the decrease (increase) of the multiple-scattering effect of the nanoparticles in the LCs, resulting in the decrease (increase) of the random lasing emission.
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