利用二階非線性光譜研究肌腱和光子能隙結構的關聯性

Abstract

在過去，許多研究顯示纖維狀膠原蛋白的二階非線性參數擁有波長的相依性。我們量測第一類膠原蛋白的二階非線性光譜並發現光譜有震盪的現象，因此我們想了解纖維狀的那一個層級結構造成二階非線性光譜的震盪。我們假設纖維狀膠原蛋白質是由水和膠原蛋白所組成周期性排列的結構，此結構類似光子能隙結構。我們利用一維光子能隙結構的理論試著去解釋光譜震盪的現象。在理論中，光子能隙結構的穿透率和態密度顯示出有震盪的現象。過去的研究發現在週期性結構中，材料本質的二階非線性參數會被增強，並且增強比例正比於此結構的態密度。如果我們用來量測二階非線性參數的波長遠離共振波長，此時材料本質的二階非線性係數可視為一個變化不大的常數。在這個前提下，我們猜測週期性結構的二階非線性光譜擁有和態密度相同的震盪週期。我們模擬纖維狀膠原蛋白在不同層級結構的穿透率和態密度，之後拿來比較我們的實驗結果。最後我們發現造成二階非線性的震盪可能來自fibril這個層級的週期性結構，而且我們模擬此層級結構的吸收光譜為217nm，這個結果很接近現實中膠原蛋白的吸收波長227nm。

In the past, several researches revealed the wavelength-dependent in the χ(2) spectra of collagen fiber. In our lab, we have found that the χ(2) spectra of type I collagen (by Chien-Min Liu) exhibits apparent spectral oscillation. We wonder which level organization cause oscillation in our χ(2) spectrum of collagen fiber. In a collagen fiber, we assume that the layered structure is composed of the water and fibrils, which was similar to the PBG structure. From the theory of one-dimensional PBG, the oscillation appears in the transmittance and density of mode (DOM). Previous investigations found the intrinsic χ(2) is enhanced proportionally to the DOM in a periodical structure. If the frequency of fundamental is far away the resonance band, the intrinsic χ(2) coefficient would be nearly a constant; therefore, the χ(2) has the oscillating phenomenon as DOM . We simulated the transmittance and DOM based on various structural hierarchical levels in collagen fiber, and then compared their oscillating period with experimental data. We found the oscillation phenomenon in our experimental data originates from the level of fibril (consists of sub-fibril and water) and its band gap is close to the absorption band (227nm) of collagen.