以高功率摻釹晶體雷射實現有效非線性轉換: 從人眼安全波段至紫外及深紫外波段

Abstract

本博士論文旨在以簡單的線性共振腔發展輕巧且穩定的高功率摻釹晶體雷射，同時利用非線性轉換的技術進一步產生波長範圍涵蓋人眼安全至紫外以及深紫外波段的雷射光源。我們考慮了熱透鏡效應，被動式Q開關準則以及寄生雷射效應優化了被動式以及主動式Q開關摻釹釩酸釔晶體雷射的輸出尖峰功率。我們也針對摻釹氟化釔鋰晶體雷射提出了數個新穎且簡便的方法來實現高功率且高能量的被動式Q開關雷射。利用脈衝式激發以及聲光晶體，我們更進一步在摻釹氟化釔鋰晶體雷射實現重複率可調的Q開關動作。 接著，我們設計了一個能夠針對腔內光學參數震盪器單獨優化且不影響基頻光光路的新穎共振腔，同時輔以被動式Q開關摻釹釩酸釔晶體雷射作為基頻光來大幅提升人眼安全雷射的輸出特性。運用相同的設計理念，我們也以摻釹氟化釔鋰晶體設計了輕巧且高效率的高能量人眼安全雷射；同時發現熱引起的雙折射效應是使等向性增益介質能夠實現有效腔內非線性轉換的主要機制。 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瓦級的紫外以及深紫外波段的高功率光源。本論文所完成的高效率非線性轉換不只讓我們可以產生波長範圍涵蓋人眼安全至紫外以及深紫外波段的雷射光源，同時並驗證了我們在優化高功率摻釹晶體雷射所設計的理念。

The aim of this thesis is focused on developing compact reliable Nd-doped crystal lasers near 1 μm 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, we take into account of the thermal-lensing effect, second threshold condition, and parasitic lasing effect to optimize high-peak-power Nd:YVO4 lasers at 1064 nm in the passively and actively Q-switched operations. We also propose practical and unique methods to successfully accomplish power scale-up of high-energy passively Q-switched 1053-nm laser with either a-cut or c-cut Nd:YLF crystals. Pulsed operations with continuously adjustable pulse repetition rate are further realized with pulsed pumped passively Q-switched and continuously pumped actively Q-switched Nd:YLF lasers. Then, we develop a separable monolithic cavity for intracavity optical parametric oscillator to remarkably improve the performance of the Nd:YVO4/Cr4+:YAG/KTP eye-safe laser at 1572 nm. The same design concept is also employed for achieving a compact and efficient high-energy Nd:YLF eye-safe laser at 1552 nm. Besides, we experimentally find that the thermally induced birefringence can lead the mutually orthogonal polarization states of the fundamental pulses to be effectively switched for accomplishing an efficient nonlinear frequency conversion without any additional polarization control. 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 355 and 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 at 1 μm.