利用超連續雷射光源進行 二階非線性光學特性之頻譜研究

Abstract

非線性光學提供非線性頻率轉換以及光學切片等等性質，使得非線性光學在 於雷射頻率轉換以及生物影像掃描上有很重要的應用。基於非線性光學現象較為 微弱，非線性頻譜研究也是一門重要的課題。不僅如此，分子的結構與非線性光 現象的產生更是息息相關，因此分子非線性光譜也拿來作為研究物質分子結構組 成的重要指標。 近年來有研究指出生物的組織結構有類似於光子晶體的排列，而非線性光學 特性的頻譜掃描或許能作為用來驗證這種結構的指標。 在這裡我們利用超連續雷射光源進行鈮酸鋰與肢內側副韌帶的二倍頻影像頻 譜掃描。我們以鈮酸鋰的二倍頻頻譜反應來修正掃描系統對於光波長的不同反應 。藉由觀察肢內側副韌帶在 700 奈米到 1200 奈米之間的二階非線性反應，我們不 僅觀察到肢內側副韌帶對於 800 奈米與 1000 奈米有良好的反應，而且還發現了有 類似於光子晶體對於二階非線性反應的規律震盪。藉由比對文獻上對於光子晶體 的敘述，不僅可以用來驗證生物光子晶體結構的存在，而且可以對於肢內側副韌 帶發生二倍頻光學現象的機制有更深一層的了解。

Nonlinear optical effects have been widely used in many criteria such as in-vivo multiphoton microscopy and new frequency generation. Due to the weakness of nonlinear optical phenomenon, nonlinear spectrum was widely investigated. Moreover, due to a close relation between molecular structure and intensity of emitted nonlinear signal, it also helps for understanding the intrinsic structure inside media, including biomaterials. About a decade ago, an enhancement of second harmonic generation found in photonic band gap (PBG) structure was introduced. The concept of bio-photonics among biomaterials may be verified by a nonlinear second-order spectral response analysis. We performed multispectral second harmonic imaging microscopy (SHIM) in lithium niobate (LiNbO3) and medial collateral ligament (MCL) with a supercontinuum laser source generated in a photonic crystal fiber. Via analyzing the calibrated second harmonic generation (SHG) spectrum, we observed not only a strong response with light of 800nm and 1000nm, but also a regular oscillation in the second-order nonlinear response of MCL very similar to that of photonic band gap (PBG) structure which indicates a possibility of bio-photonics. However, there are still some works left for further confirm of bio-photonics by multispectrocopy.