利用飛秒脈衝雷射其高頻調製與波長可調性於漫反射光譜學之應用

Abstract

在本論文中，我們使用了飛秒脈衝雷射的超寬頻寬和高尖峰功率兩個特性，來突破頻域調變擴散光譜學(Frequency Domain Photon Migration Spectroscopy)中的調變頻率限制和操作波長限制。在調變頻率方面，我們在實驗中使用了鎖模雷射的高階調變項。因此在GHz調變頻率時，激發光源還可以維持一定的調變深度。另一方面，藉著光子晶體光纖中的種種非線性效應(Cherenkov radiation and Raman shift)，激發雷射光源可以有效率的往長波長與短波長方向轉換，而不需使用多台雷射來做為激發光源。此新穎的雷射使用，大大地增加頻域調變擴散光譜學的操作波長範圍與調變頻率範圍，並也大大地減少量測時間和成本。其次，我們用這多波長(700 nm~1300 nm)、寬頻寬的光源，搭配頻域調變擴散光譜學系統，實際取得生物組織或樣本的相關吸收與散射參數。最後，我們也提出了將光源部分，連接一段長光纖，使用光纖的色散效應，使脈衝在時間上的拉寬。將光源能量分佈在窄的頻域裡。此方法可以進一步提升在某一些調變頻率的能量，未來在深層的生物組織量測中，非常具有應用價值。

In this thesis, femtosecond laser pulses, intrinsically with wide bandwidth and high peak power simultaneously, are utilized in frequency domain photon migration (FDPM) spectroscopy. First, the modulation frequency limit arising from traditional cw-modulated lasers in FDPM systems is break out by using the higher-order modulations of mode-locked laser pulses. Second, the restrictions on the operation wavelength in a single light source are utilized by a photonic crystal fiber (PCF) wavelength converter, where the excitation 1030 nm pulses are efficiently transformed toward the shorter and longer wavelength regimes via various fiber-nonlinear effects. The FDPM spectroscopy with GHz modulation bandwidth and a wide wavelength tunability in the 700 nm to 1030 nm were also demonstrated in the thesis. Finally, we also proposed and demonstrated a preliminary result that the SNR can be enhanced by increasing the pulse width through fiber dispersion. in biological tissue or sample.