腔內倍頻準相位匹配綠光雷射之研究

Abstract

本篇論文主要可分為準相位匹配原理的介紹、週期性極化反轉鈮酸鋰晶體的製作，以及腔內倍頻準相位匹配綠光雷射系統架設等三大部分。 首先在原理部分，我們簡單的介紹了非線性頻率轉換，與準相位匹配的理論。 接著在製程部分，本文介紹了本實驗室建立的高電壓極化反轉系統，並詳細說明了改良後的光微影製程方式，目前已可以在厚度500 m的鈮酸鋰與鉭酸鋰基板上，成功的製作出綠光倍頻波段，週期分別為6.67 m與7.7 m的1D-PPCLN、2D-PPCLN與1D-PPCLT、2D-PPCLT晶體。另外，也詳細的介紹了微米小球微影術在週期性反轉鈮酸鋰上之應用，成功的製作出高深寬比的極化反轉結構。 最後在光學量測的部分，本文先以波長1064 nm脈衝雷射對週期為6.67 m的1D-PPCLN做二倍頻量測，在未做抗反射鍍膜的情況下量得30%的轉換效率，且證實有效長度已達到製作的6 mm。接著再以此1D-PPCLN晶體架設腔內倍頻準相位匹配綠光雷射，其輸出效率已達到一般以KTP製作的腔內倍頻綠光雷射的兩倍左右，證實了準相位匹配高轉換效率的機制。

This thesis is organized into three parts: (a) an introduction to the theory of Quasi-Phase Matching (QPM) theory, (b) the design and fabrication of Periodically Poled Congruent-grown Lithium Niobate (PPCLN, LiNbO3) and Lithium Tentalate (PPCLT, LiTaO3), and (c) the implementation of intra-cavity QPM green laser. Three fabrication methods of PPLN/PPLT were investigated in this work. They include (a) an improved photo-resist poled method, (b) poling with surface domain inversion, and (c) poling with self-assembled micro-sphere lithographic patterns. Results of periodical poling through 500 m-thick CLN/CLT with a periodicity of 6.67 m/7.7 m were achieved by methods (a) and (b)；whereas high aspect ratio of poled domains can be achieved in the method (c). A single-pass second-harmonic generation (SHG) characterization of a 6 mm-long 1D-PPCLN by a Nd:YAG 1064 nm/26 ns pulsed laser exhibits a conversion efficiency of 30% at a pump intensity of 26.5 MW/cm2. For implementation of an intra-cavity SHG green laser, we achieve a continuous wave operation of QPM-SHG green PPCLN laser that emits 60 mW power at a 1W pump power from a 808 nm diode laser. This figure is about twice that of a conventional intra-cavity SHG green KTP laser tested under the same cavity structure.