| Summary: | 碩士 === 國立中山大學 === 光電工程學系研究所 === 102 === Compared with conventional lasers, random lasing can be generated by using an active medium and scattering materials without any requirement of fixed reflection mirrors to form a cavity. The scattering materials can provide multiple light scattering paths to form scattering loop paths for random lasing. Lasing emitted from such mechanism provides some unique characteristics, such as the multi-mode lasing, multi-direction emission, simple manufacturing process, and small device sizes. Therefore, random lasing leads to many potential applications for lighting, spackle-free imaging, miniature light source in integrated photonic circuits or medical arena.
In this thesis, random lasing with resonant feedback can be observed from a 20μm-core hollow optical fiber filled with dye-doped liquid crystals(DDLCs) containing nanoparticles. At the same time, the tunable emission properties of the generated random lasing is realized by changing the operation temperature and the applied electric field. Besides, the generated lasing emission can be confined in the fiber core by the total internal reflection effect with a fixed direction, which can reduce the losses while measuring the emission signals. We found that the threshold pumping energy of the DDLC with nanoparticles in fibers can be effectively reduced. The threshold pumping energy can be reduced about 2.95μJ/mm2 by doping BaTiO3 nanoparticles, and 12.91μJ/mm2 of threshold pumping energy can be reduced by doping Ag nanoparticles. We have also observed that the emission wavelength and intensity can be controlled by the operation temperature. In addition, the emission can be switched between resonant random lasing and non-resonant random lasing by applying the external electric field.
Finally, to obtain the optimum lasing efficiency, we observed DDLCs containing different concentrations of nanoparticles. Optimum lasing efficiency can be obtained by using 0.3wt% BaTiO3 nanoparticles with 27.56μJ/mm2 threshold pumping energy, and by using 0.4wt% Ag nanoparticles with 16.27μJ/mm2 threshold pumping energy.
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