頻譜解析三倍頻顯微術之模擬研究

Abstract

三倍頻顯微術奠基於發展已久之非線性生成理論，當光與物質的時間範圍接近時，物質的時間反應函數則不可忽略須一併計算。本論文經由數值模擬計算電場與物質的電極化率的時間函數，模擬實驗上可得之寬頻鉻貴橄欖石雷射光譜與存在生物體內之亞油酸交互作用後之三倍頻頻譜，在此模型中我們可知有六項變因會使頻譜的形狀與強度皆有所改變，分別是入射光的脈衝寬度、波包形狀、二階及三階色散、物質的相位緩和時間常數、共振對非共振比例以及共振波長，在調變不同變因時，我們以無共振所生成的頻譜當作強度基準，配合模擬計算得知三倍頻頻譜以及亞油酸共振項所產生的三倍頻頻譜，當我們定義亞油酸共振所產生的三倍頻比雷射產生的三倍頻大時，可以使得共振項在頻譜上被解析出來，如此我們可以得知此六項變因的可接受範圍，以實現頻譜解析三倍頻顯微技術。

By computing the response function of the electric field and the nonlinear susceptibility, I build up a simulation model for the numerical study of third harmonic generation microscopy based on the non-instantaneous third harmonic generation process for the case the response times are comparable. Based on the IR spectrum of a broadened Cr:forsterite laser and the absorption spectrum of a possible contrast agent, linoleic acid, we found six parameters including field pulse-width, envelope form, second-/third-order dispersions, de-phasing times, resonant to non-resonant ratios, and resonant wavelengths that could affect the response function, thus would change the resulting third harmonic generation (3HG) in both intensity and shape spectrally. Since we are aimed at identifying the molecular resonance in 3HG spectrum, the ratio of the intensity at one-third of medium resonant peak over the intensity at one-third of laser peak were calculated. By finding the range the intensity ratio is larger than 1, we could obtain the acceptable range of the parameters for resolving the spectral characteristics of resonant components which makes possible the spectrally-resolved 3HG microscopy.