利用受群速度色散扭曲之頻率解析光柵重建超短脈衝頻域相位之方法

Spectral Phase Retrieval by Dispersion-distorted Frequency-resolved Optical Gating Traces

吳博雅(PO-YA WU)

指導教授 ： 楊尚達

國立清華大學/電機資訊學院/光電工程研究所/碩士(2015年)

https://doi.org/10.6843/NTHU.2015.00568

摘要

本研究旨在探討厚非線性晶體中嚴重的群速色散以及其對二倍頻頻率解析光柵Second-Harmonic-Generation Frequency-resolved Optical Gating (SHG FROG)圖形的扭曲，並提出應用粒子群演算法之最佳化方法，以迭代演算重建基頻脈衝之頻域相位以及時域波形，讓擁有高非線性轉換效率之厚非線性晶體得以被應用在準確的飛秒脈衝量測上。實驗上應用25-fs Ti:S laser、Aperiodically Poled Lithium Niobate (APPLN)厚晶體(15mm)以及穿透式脈衝塑型器干涉儀之架構以取得頻率解析光柵圖形。本研究在電腦模擬以及實驗上均成功重建特殊脈衝相位及波型。

關鍵字

頻率解析光柵 ； 群速度色散 ； 超快光學 ； 非線性光學

並列摘要

Crystal nonlinearity is a widely employed technique in measurements and analyses of femtosecond pulse lasers. To solve the Group Delay Dispersion (GDD) problem and enable the proper usage of thick crystal, which possess excessively high conversion efficiency, in pulse measurements, we thoroughly examine the Second-Harmonic-Generation Frequency-resolved Optical Gating (SHG FROG) traces strongly distorted by excessive GDD. The SHG FROG traces from fundamental pulse with short pulse duration (25fs) in thick Aperiodically Poled Lithium Niobate (APPLN) crystal (~15mm) are considerably different from the standard SHG FROG traces, indicating that GDD severely influences the FROG traces and the standard retrieving method of phases of fundamental fields in SHG FROG is no longer applicable. Here we introduce a new retrieving method making use of the GDD-distorted FROG traces and applying the iterative optimization algorithm: Particle Swarm Optimization (PSO), which allows us to successfully retrieve the spectral phase of the fundamental pulse. In the experiment, we apply a 15mm APPLN as the nonlinear crystal to demonstrate serious GDD effect and meanwhile obtain a PM spectrum that is sufficient for 25-fs Ti:S laser as fundamental pulse. A shaper-assisted interferometer with collinear output beam duplicates is set to scan the GDD-distorted FROG traces with APPLN. The experimental results prove the strength and usefulness of this retrieving algorithm and unprecedentedly demonstrate pulse retrieval using thick crystal and under severe GDD.

並列關鍵字

Frequency-resolved Optical Gating ； Group Delay Dispersion ； Ultrafast Optics ； Nonlinear Optics

參考文獻

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