端面激發Q開關固態雷射之優化與波長轉換

Abstract

本博士論文旨在以簡單的線性共振腔發展輕巧、穩定且高品質的高功率、高能量摻釹晶體之Q開關雷射，同時利用非線性轉換的技術進一步地將基頻光做波長轉換，進而產生波長範圍涵蓋人眼安全至綠光、紫外以及深紫外波段的雷射光源。我們特別對摻釹釩酸釔和摻釹氟化釔鋰以及摻釹釔鋁石榴石晶體的特性做詳盡的介紹，同時針對主動式與被動式Q開關雷射所面臨的不同議題分別提出獨特且創新的設計概念去加以研究並改善其輸出效能而達到優化之目的。 首先，我們設計了一個極輕巧且可調能量的被動式Q開關微型雷射。接著，我們考慮了熱透鏡效應、被動式Q開關準則以及高階橫向模態的影響，優化了被動式Q開關摻釹釔鋁石榴石晶體雷射在空間上與時間上的輸出表現，並更進一步的提升其輸出尖峰功率。再者，我們利用了高效率的腔內光學參數震盪器共振腔，同時輔以主動式Q開關摻釹氟化釔鋰晶體雷射作為基頻光來完成了輕巧且高效率的高能量人眼安全雷射。 此外，利用優化過後的摻釹晶體近紅外雷射搭配腔外諧波產生的技術，我們也進一步產生波長範圍落在綠光、紫外光、以及深紫外波段的雷射光源。在相同的環境條件下，我們比較了腔外以及腔內架構在產生二倍頻綠光時的轉換效率。我們接著以腔外三倍頻以及四倍頻的方法有效地產生紫外的高能量光源以及深紫外波段的高功率光源。 最後，我們也利用了一個新穎的光源─『二維的垂直共振腔面射雷射陣列』系統作為激發光源，分別針對摻釹釩酸釔和摻釹氟化釔鋰晶體雷射在半球形共振腔以及全球型共振腔的架構下，考慮個別晶體在Q開關系統中的優化條件，進而研究並提升該雷射系統在空間中以及時間上的輸出表現。 由於這些特殊波長的獨特性，我們相信本文所發展的高功率綠光與紫外光雷射抑或是高能量人眼安全波段雷射無論是在學術發展或是產業應用皆能夠提供相當大的幫助與價值。除此之外，上述的成果也同時並驗證了我們在優化Q開關摻釹晶體雷射所設計的理念。

The aim of this thesis is focused on developing compact reliable Q-switched Nd-doped crystal lasers based on linear cavity configuration, and these optimized near infrared lasers are subsequently applied for several nonlinear frequency conversions to effectively extend the spectrum from eye-safe to deep ultraviolet regimes. First of all, an energy adjustable passively Q-switched laser is demonstrated with a composite Nd:YAG/Cr4+:YAG crystal. We also exhibit a specially designed Nd:YAG/Cr4+:YAG miniature laser, which is constructed to manifestly show that the scale-up of the pulse energy without the negative effect due to the higher-order transverse modes can be practically realized by increasing the pump radius and setting the corresponding critical cavity length simultaneously. Then, we originally utilize a nearly hemispherical cavity to accomplish the energy scale-up for a high-repetition-rate nanosecond pulsed pumped Nd:YLF laser passively Q-switched by the Cr4+:YAG saturable absorber. Moreover, we employ the intracavity optical parametric oscillator to achieve a compact and efficient high-energy Nd:YLF eye-safe laser at 1552 nm. A novel system of 2D VCSEL arrays end-pumping module is utilized for realizing stable, high-quality, and high-energy Nd-doped PQS lasers. Finally, the optimized Q-switched Nd-doped crystal lasers are employed to produce green, ultraviolet, and deep ultraviolet radiations via extracavity harmonic generations. We first compare the output performance between the extracavity and intracavity second harmonic generations at 532 nm under a similar operated condition. We further perform extracavity third and fourth harmonic generations to effectually produce ultraviolet waves at 351 nm as well as deep ultraviolet radiation at 266 nm with output powers up to several watts. Efficient nonlinear frequency conversions not only enable us to produce the emission wavelengths from eye-safe to deep ultraviolet regions, but also confirm the usefulness of our cavity design for Q-switched lasers.