利用週期性極化反轉結構產生高階和頻諧波

Generation of high order harmonics by sum frequency mixing in periodically poled structure

沈欣怡(Shin-Yi Shen)

指導教授 ： 孔慶昌

國立清華大學/電機資訊學院/光電工程研究所/碩士(2012年)

https://doi.org/10.6843/NTHU.2012.00099

摘要

本研究重點為利用模擬來設計週期性極化反轉鉭酸鋰多段式晶體，期望達成多個諧波同時輸出，拓展現有的多諧波輸出技術，增寬頻譜範圍使脈衝壓縮的更短。配合合成波形技術，達到次飛秒的超短脈衝光源，更加接近有效觀察及控制電子運動的目標。本篇論文主要分為光參振盪器及準相位匹配之理論介紹、模擬和設計非線性晶體、製出晶體之量測結果與分析，在論文最後附上可程式化全光譜雷射波長轉換系統的晶體效率量測。
理論部分介紹非線性頻率轉換、光參振盪器及準相位匹配。晶體設計與量測部分，介紹了晶體各段週期的計算，接著藉由一種特殊型式週期分佈的非線性晶體實際量測晶體週期，決定多段式晶體週期的佈局，再由程式模擬出有最佳轉換效率輸出的長度搭配，成功配製出一多段式晶體可以同時達到七個準相位匹配的諧波輸出。最後附件為量測和頻與差頻晶體的轉換效率，協助龍彩科技股份有限公司開發可程式化全光譜雷射波長轉換系統，然而差頻晶體的量測以超過1%的轉換效率突破文獻所達最高轉換效率。

關鍵字

非線性 ； 週期性極化反轉

並列摘要

This research focuses on simulating and designing a chip with periodic poled congruent grown lithium tantalite to achieve the goal of multiple harmonics generation simultaneously so as to expand the range of spectrum of the laser wavelength. With the technique of waveform synthesis, this chip will allow us to obtain ultrashort subfemtosecond pulses. It will make the ultimate goal of controlling electronic motion closer to reality. The thesis includes a short summary of the theory of optical parametric oscillator (OPO) and quasi-phase matching (QPM), simulation and design of the nonlinear crystal, measurement results and analysis. At last, there is an attachment about the conversion efficiency measurements of crystals designed for a programmable full-spectrum laser wavelength conversion system.
In the first part, we introduce frequency conversion, OPO and QPM. In the part of measurement and design, we calculate the phase-matched periods, test the fan-out chips and simulate conversion efficiencies to decide on the periods and lengths of every section on a QPM chip that can be sued for multiple harmonics generation. We successfully designed and fabricated a chip that can generate seven harmonics. In the last part, we describe the measurement of the conversion efficiencies of sum frequency generation (SFG) and difference frequency generation (DFG) of a CW fiber laser and a 1550 nm laser diode for the purpose of building a programmable tunable laser source. The conversion efficiency of DFG is 1.21% which is higher than any reported in the literature.

參考文獻

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