非 線 性 光 譜 與 顯 微 術 之 研 究

Abstract

本論文包含一些關於非線性光譜術與顯微術方面的研究。在非線性光譜術方面，我們探討的題目有二：其一為非線性光譜分析中的相位回復問題，另一個則為和頻光譜技術用於研究分子手徵性的相關研究。在本論文中，我們探討最大熵值相位回復法如何應用於解決非線性光譜分析中的相位回復問題。我們發現當光譜中包含非共振背景貢獻時，其誤差相位的行為會受到影響。這會影響我們在最大熵值相位回復法中估計誤差相位所需採用的近似法。另外我們也發現最大熵值相位回復法的一個新的應用----它可以用來解決在使用富利葉轉換極限脈衝所量得的光譜分析中，在做逆折疊運算時所遭遇的相位回復問題。在研究分子手徵性的應用方面，我們應用和頻光譜技術研究一個具手徵中心的液晶分子，結果發現一個甲基的振動行為會受相鄰的手徵中心所影響。左旋光與右旋光強度的差異與平均比可高達百分之五十。在非線性顯微術方面，我們建構一架皮秒級半導體雷射光泵固態鎖模雷射當作二倍頻顯微鏡的激發光源，並且用此二倍頻顯微系統來檢測受到橫向電場極化之非線性高分子薄膜與週期性極化的鈮酸鋰晶體中與微米尺度的二倍頻強度分佈情形，從二倍頻顯微術中所量測到的二倍頻強度分佈，我們可以獲得關於非線性分子在薄膜中的排列情形以及鈮酸鋰反轉區域的分佈狀況。

In this thesis, we studied several important topics on nonlinear optical spectroscopy and microscopy. As for nonlinear optical spectroscopy, we studied how a phase-retrieval procedure based on the maximum-entropy method is applied to the coherent nonlinear optical spectra. The error-phase behavior was found to be influenced by the interference between the resonant part and a nonresonant background. This result implies that the estimation of the error-phase, the key-step in the whole phase-retrieval procedure, will depend on the nonresonant-background contribution. We also discovered a new application of the maximum-entropy phase-retrieval procedure. This method can solve the phase retrieval problem in the deconvolution process for nonlinear optical spectra measured with transform-limited light pulses. On the other hand, we also presented the potential of the infrared-visible sum-frequency spectroscopy in studying the molecular chirality. An experimental spectra from a chiral liquid crystal showed that the vibrationally stretching mode of a methyl group will be affected by a nearby chiral center. Therefore the local mirror-asymmetry can be measured by using methyl group as a probe. The normalized intensity difference between left- and right-hand circularly excitation in the measured spectrum was found to be as high as 50%. As for the nonlinear optical microscopy, our studies were focused on the second harmonic microscopy. We constructed a pico-second diode-pumped solid-state-laser as the exciting source for the second harmonic microscope. We applied the second harmonic microscopy to the characterization of a in-plane electric-field-poled polymer and a periodically poled lithium niobate crystal. From the recorded second harmonic intensity pattern, we can deduce the information about the local orientation of the nonlinear optical molecule in the poled polymer and the inverted domain structure in a periodically poled lithium niobate crystal.