| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 97 === In comparison with the traditional high power lasers, fiber lasers provide several advantages, such as extremely high optical conversion efficiency and better beam quality which is closed to the diffraction limit. From the aspects of compactness and heat dissipation, the usage of the active fiber has a great commercial potential, which can reduce the operating cost and maintenance fee. For the applications of manufacturing, nonlinear optics and laser plasma, it has a great possibility to replace the traditional high power laser. For the progress of the fiber laser, thousands watts of single mode continuous wave (CW) output power has already existed. Besides, the multi-mode fiber laser has achieved the level of ten thousands of watts, and the pulse fiber amplifier is gradually on the progress.
In this thesis, a nearly hundred-watt-level ytterbium fiber laser is demonstrated, and the experimental data agree well with the simulation result. The optical conversion efficiency is over 50%, and the beam quality factor is 1.22, which is a stable laser source, being suitable for the direct second harmonic generation (SHG). Furthermore, there is a discussion about the birefrigent phase matching condition and the choice of LiB3O5 as the nonlinear crystal for the SHG. Under the condition of focused Gaussian beam, there exists an optimized solution to fit the SHG conversion efficiency. In addition, through the experiments, it is proved that the theoretically optimized focusing condition has the greatest CW SHG output power. Moreover, the CW SHG power is stable to maintain at least 300 mW for an hour, with the beam quality factor closed to 1.76. All the experimental data had convinced that the ytterbium fiber laser is a good platform for direct frequency doubling.
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