在這個實驗中，我們建立了一套中紅外差頻光雷射光源，波長的可調範圍為3.99 μm到4.17 μm，而在 4.19 μm波段能量輸出的最大值為 3 mW。並將此中紅外光源耦合進一條空心光纖中，做二氧化碳R (60)的飽和吸收光譜量測。
本論文分成兩大部分，第一部分為利用一台可調波長(840-868 nm)的主振盪器配功率放大器雷射搭配一台Nd:YAG雷射(1064 nm)和10W 的光纖放大器，經過週期性極化反轉鈮酸鋰(PPLN)晶體來產生中紅外差頻光，第二部分為飽和吸收光譜的實驗架設，將產生的中紅外光源耦合進一條長1公尺直徑300 μm的中空光纖中，並用一凹面鏡反射回光纖中做探測光量測二氧化碳分子在基頻帶 00^0 1←00^0 0 R(60) 躍遷譜線的飽和吸收光譜，同時分析其吸收譜線的Lorentz線寬。此外，我也將差頻光束截面和經中空光纖後的差頻光截面做一系列的探討。
未來，我們希望能改善差頻光的能量轉換效率，及以一短焦距的BaF2透鏡增加中空光纖差頻光的耦合效率，並且利用鎖相放大器和PID將主振盪器配功率放大器雷射的頻率鎖在二氧化碳 R(60) 的三階微分訊號上。

In this experiment, we build up a new difference frequency generation laser source with the wavelength tuning range from 3.99 μm to 4.17 μm, and the maximum output power is 3 mW at 4.19 μm. Then, we couple the mid-infrared light into the hollow core fiber to measure the saturated absorption spectroscopy of CO2 R(60) transition.
In this thesis, I separate the entire experiment into two parts. The first part is talking about the DFG source, we build up the source with a tunable cw MOPA laser (840-868 nm) and a Nd:YAG laser (1064 nm) with the 10 W fiber amplifier. Two laser beams passing through the Periodically Poled Lithium Niobate (PPLN) crystal generate the DFG source. The second part is the experimental setup of saturated absorption spectroscopy, we couple the mid-infrared light into a hollow core waveguide, 1 m long with the diameter 300 μm, and re-coupled via the concave mirror to serve as the probe beam, and measure the saturated absorption spectroscopy of CO2 R(60) transition on the fundamental band 00^0 1←00^0 0. Simultaneously, analyze the absorption linewidth with Lorentz function, and also record and discuss the beam profiles in this thesis.
In the future, we are going to optimal the energy conservation efficiency, change a BaF2 lens with shorter focal length to increase the coupling efficiency, and use lock-in and PID to lock the frequency of MOPA laser on the zero-crossing point of third-derivative saturation dip of CO2 R(60) transition.

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