低同調雷射光源技術研究與應用

Abstract

本篇論文以三大部分構成：準相位匹配、光參振盪器及雷射散斑原理的介紹、光參振盪器晶體及倍頻綠光晶體之設計，和光參振盪器頻譜分析、綠光倍頻實驗、寬頻綠光空間分布及雷射散斑量測。 理論的部分，由簡入繁地介紹了非線性頻率轉換、準相位匹配、基本的光參振盪器理論與散斑概述。接著在鉭酸鋰光參振盪器晶體週期設計的部分中，不同於以往單週期7.63 um 設計，設計出以三個週期7.63 um、7.64 um、7.65 um 的並聯方式，讓光束一次通過三個週期，並進行排列組合且週期和週期間有10 um 的狹縫；而倍頻綠光晶體極化反轉週期為5.495-9.845 um。 在光學測量的部分，利用薄平面鏡作為Fabry Perot 濾光鏡，使其作為光參振盪器的輸出鏡以產生梳狀的寬頻紅外光譜，並量測各種不同週期排列的頻譜，得到週期7.65_7.63_7.64 um 在132°C有最寬頻70 nm。接著利用寬頻紅外光通過多週期鉭酸鋰以產生寬頻綠光雷射，比較了不同方向入射及不同啁啾率(Chirp rate)，得到PPLT SHG 1010 mm Long Short Long Short 有最寬頻47 nm。最後利用此寬頻綠光進行空間分布分析及散斑對比值(SC)的量測比較，得到寬頻綠光散斑對比值小於5%，成功開發出低同調光源。

This thesis is organized into three parts : (a) the theory of quasi-phase matching, quasi-phase matched optical parametric oscillator (QPM OPO), and speckle (b) the design of transversely-displaced three-QPM structures in periodically poled LiTaO3 (PPLT) for constructing 1064nm broadband OPO laser and a multi-chirped PPLT device for generation of broadband green laser (c) implementation of a QPM-OPO system, second harmonic generation (SHG) experiment, spatial distribution of laser beam intensify and speckle reduction with broadband green lasers. First, the theory of QPM, OPO and speckle is introduced in chapter 2, chapter 3 and chapter 4. In the second part, the designed periods of PPLT is introduced. A 532 nm nano-second laser pumped 1064 nm broadband OPO is achieved by simultaneously the exciting tri-QPM structures in parallel with each periodicity of 7.63, 7.64, and 7.65 um, respectively, and 200 um width and 10 um spacing. The chirped periods for constructing broadband green lasers is from 5.495 to 9.845 um. Finally, based on the Fabry Perot effect, a thin flat is used as the output mirror for the OPO to construct a broadband infrared frequency comb. The output OPO spectrum for the period 7.65_7.63_7.64 um design has the largest spectral bandwidth of 70 nm at 132°C. The IR combs are then used as fundamental source to pass through the multi-period chirped PPLT for generate of broadband green lasers. For comparison, pumping from two different directions and two different chirp rate are studied. The output spectrum for PPLT-SHG 1010 mm Long Short Long Short sample gets the broadest bandwidth of 47 nm. Moreover, using this broadband green laser to implement the analysis of spatial distribution and speckle. The resulting of speckle contrast ratio below 5% by engineering the low temporal-and-spatial coherence of the laser source.