週期性極化反轉鈮酸鋰晶體中極化與非極化區域之正反向倍頻比較

近年來，雷射的應用與需求日益廣泛；但由於雷射光源在波長上仍有缺乏，故藉由準相位匹配(Quasi-Phase matching, QPM)的技術，使用非線性材料做頻率轉換而產生此波段雷射，已經成為主要方法之一。週期性極化反轉鈮酸鋰(periodically poled lithium niobate, PPLN)在非線性光學領域中是重要的材料，若週期性極化鈮酸鋰晶體中極化與非極化的週期性結構良好，則可以有很好的非線性轉換的效率；但是對於週期性極化鈮酸鋰晶體內部之結構好壞的判定，目前卻沒有一套適用的方法。我們必須知道是否有方法能夠清楚反應出有關晶體內部結構的資訊，才能藉此幫助判斷一塊週期性極化鈮酸鋰晶體在結構上的好壞。二倍頻能夠反映出晶體的分子結構，因此我們利用倍頻顯微術來觀察週期性極化鈮酸鋰晶體內部在穿透與反射頻道的倍頻影像。我們發現在極化反轉的製程中使得鈮酸鋰晶體結構產生了變化。在均勻的鈮酸鋰塊材中，是觀測不到倍頻訊號的；但在外加不均勻電壓的極化製程後，我們在週期性反轉鈮酸鋰晶體中間發現倍頻，並且進一步證明在極化區域所外加的電壓對於製程預定之非極化區域有所影響。而在製程中外加均勻電壓的週期性反轉鈮酸鋰之中，無論極化反轉區域或非極化反轉區域，皆被觀察到與塊材相同的表現。我們證明了製程中外加電壓的均勻度會影響到週期性反轉鈮酸鋰晶體中間結構的好壞；此外，我們也詳細比較了週期性極化反轉鈮酸鋰在極化區域與非極化區域的正反向倍頻表現。我們對於將倍頻顯微技術應用在晶體結構之分析檢測上提供一個實際的方向，並且在未來很適合應用於輔助週期性反轉製程的改進。

關鍵字

非線性光學；倍頻顯微術；鈮酸鋰；二倍頻

並列摘要

In recent years, laser has been wildly used in many applications. Because of the lack of laser source in certain wavelength, generating new light source in nonlinear materials by the quasi-phase matching technique (QPM) becomes one of the most important methods. Periodically poled crystal (PPC) is one of the most attractive materials in nonlinear optics due to its high nonlinear conversion efficiency. Good crystal structure leads to good nonlinear conversion efficiency. However, the crystal quality is only judged by observing spatial stability of the period before. There has been no study tries to give the internal micro-crystal structure information in both poling and non-poling domains of periodically poled crystals. Note that molecular structure of crystal affects second harmonic generation (SHG) signals, we choose second harmonic microscopy to observe PPC. Both the forward and backward second harmonic images are analyzed. In this study, we prove that the crystal structure is changed during poling process and also discussed the relation between the applied electric field in the process and the SHG intensity in PPLN. Furthermore, we compare the SHG performance between poling and non-poling domains in both forward and backward channels and pointed out the difference between these two domains. We believe that this study is very helpful for the improvement in fabrications of PPC in the future.

並列關鍵字

nonlinear optics ； second harmonic microscopy ； lithium niobate ； second harmonic generation

參考文獻

[9] 盧昶伸, 準相位匹配鈮酸鋰光學參量振盪器之研究. 國立台灣大學光電工程學研究所碩士論文(2007)

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[2] R. W. boyd, Nonlinear Optics, Elsevier, New York(2007)

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[5] J. A. Giordmaine, “Mixing of Light Beam in Crystals,” Phys. Rev. Lett. 8, 19-20(1962)

國際替代計量

週期性極化反轉鈮酸鋰晶體中極化與非極化區域之正反向倍頻比較

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