臺灣博碩士論文加值系統

相對Nd:YAG常用於傳統高功率固態雷射作為增益介質，Yb:YAG具有較小的量子缺陷，較寬的吸收、輻射頻寬，較長的自發輻射生命期，使用在Q開關雷射中可累積更多的能量。此外，Yb:YAG可摻雜較高的離子濃度，增益介質的長度可以減小，進而減少光路的偏移量及環形共振腔內穩定性的破壞，使得Yb:YAG晶體更適合用在雙鏡式環形共振腔雷射系統中。

由於Yb:YAG屬於準三能階雷射，因熱效應所產生的重複吸收損耗是影響準三能階雷射輸出功率的重要因素，此效應會降低雷射的斜率效率，故本實驗目的在改善原有架構的散熱效率，以及改變增益介質長度，配合上不同迴圈穿透率的耦合透鏡，將雷射的斜率效率提升至50.3 %。本論文並嘗試以銅鋁包覆Yb:YAG晶體光纖，與原有的雙鏡式環形共振腔結合成新的架構，故有關Yb:YAG晶纖之製程與雷射元件之機械製備和其光學鍍膜設計等在本文中將作詳細說明，並且介紹Yb:YAG晶纖環形雷射的實驗成果。

此外，本實驗使用數值分析中的有限時域差分法來解析Yb:YAG環形被動式Q-開關雷射的速率方程式，模擬Q-開關雷射的重複頻率、脈衝寬度、脈衝峰值功率，希望藉此掌握各個影響雷射性能的重要參數，以最佳化雷射的效率。

Though Nd:YAG has been widely used as the traditional high power solid-state laser gain medium, Yb:YAG has more advantages such as lower quantum defect, wider absorption and emission bandwidth, and longer fluorescence lifetime, which can be used in Q-switched lasers to storage more energy. In addition, a higher doping concentration Yb:YAG with thinner thickness reduces the shift of optical path, which reduces the ring cavity stability. Therefore Yb:YAG is an eminently suitable gain medium for the two-mirror ring laser.
Due to the quasi-three-level characteristic of Yb:YAG, the thermal effect influences the re-absorption loss and deteriorates the laser performance, i.e. lower slope efficiency of laser. In this thesis, we improve the laser efficiency by using Yb:YAG crystal with proper thickness, and various round-trip transmittances with different output couplers were tried. The slope efficiency with 50.3 % has been achieved. We also tried to reduce the thermal loading of Yb:YAG by crystal fiber with Cu-Al alloy package. The fabrication process of Yb:YAG crystal fiber, including sample preparation, and coating design, and the experiment result of Yb:YAG crystal fiber ring laser will be presented in detail.
Furthermore, we use numerical analysis to modify the passively Q-switched Yb:YAG ring laser rate equation with FDTD (finite difference time domain) method. The simulated repetition rate, pulse width and peak power were compared to the experimental results in order to optimaize laser performance.

目錄

中文摘要 i
英文摘要 ii
目錄 iii
圖目錄 v
表目錄 viii

第一章 緒論 1
第二章 Yb:YAG環形雷射原理 3
2.1 雙鏡式環形共振腔再入射條件 3
2.2 增益介質Yb:YAG 9
第三章 Yb:YAG環形雷射 17
3.1 雷射架構 17
3.2 雷射效率提升 18
3.2.1 溫度影響 18
3.2.2 迴圈穿透率的影響 25
3.2.3 增益介質長度的影響 29
3.3 Yb:YAG 環形雷射實驗結果 30
第四章 Yb:YAG晶體光纖環形雷射 33
4.1 晶體光纖製備 33
4.1.1雷射加熱基座生長法 33
4.1.2銅鋁合金包覆及研磨、拋光 37
4.1.3 光學鍍膜 43
4.2 雷射架構與實驗結果 45
第五章 被動式Q開關Yb:YAG環形雷射數值模擬 49
5.1 理論模型 49
5.2 實驗結果與分析 56
第六章 結論 59

參考文獻 61
中英對照表 64
附錄 A : 被動式Q開關Yb:YAG環形雷射數值模擬 66
附錄 B : Yb:YAG碟形雷射(Thin disk laser) 73

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