由於氦原子結構簡單、化學特性穩定，氦原子常常是討論原子分子多體運動的基本原子，其光譜線的精密量測結果，用於驗證理論計算、驗證數學近似法的準確度檢驗有著重大的幫助，另外，氦原子也是太空中常見的粒子，其光譜也廣泛的被應用在天文物理上。
　　都普勒增寬問題是研究精密光譜量測重要一環，為了克服都普勒增寬，常見的光譜學方法為：雙光子光譜，飽和吸收光譜，電磁誘發透明光譜等．．．。本篇目的是利用飽和吸收光譜觀測氦原子2S-3P的精細結構。為此我們架設了一套完整個光學系統，包含：雷射光源部分、倍頻系統與溫控器、氦原子的放電系統、Fabry-Perot共振腔以及量測系統。
利用以上的系統我們成功的觀察到氦原子2S-3P的各種譜線，包含: 督普勒吸收光譜、2S-3P的精細結構分裂譜線。其中，2S-3P的精細結構分裂譜線包含了 J=0、J=1、J=2三條譜線外，也觀察到了三條crossover的現象，共六條譜線。我們分析譜線的線寬，頻率距離以及對光譜進行fitting，皆得到與理論相近的結果，因此我們可以確定觀察到的譜線是氦原子2S-3P的精細結構。
最後，我們也對吸收光譜與飽和吸收光譜的訊號強度對各種參數進行參數相依的實驗，這些參數包含:壓力、光強度、放電功率等等．．．。目的是為了確認各種參數的變化對光譜的訊號強度的影響，以便於日後最佳化訊號強度，提升訊噪比及優化系統時，能夠給予一定的參考標準。
關鍵字：飽和吸收光譜。

The structure of helium atoms is simple and stable, so that helium atoms are regarded as the fundamental particles in the field of many-body problems. Helium spectrum play an important role on theoretical examination and physical model checking. On the other hand, helium can be easily found in outer space, the spectrum of helium are widely used in the field of astrophysics.
Doppler broadening is an important problem in the field of high precision measurement. There exists many kinds of methods to overcome this problem of Doppler broadening such as saturation absorption spectrum, two photon transition spectrum, and electromagnetically induced transparency spectrum, and so on... The research purpose of this thesis is to observe the Doppler-free spectrum of helium 2S-3P transitions. For this reason, we construct an optical system that include laser source, frequency doubling system, helium discharge system, Fabry-Perot cavity and saturated absorption spectroscopy.
We observed both absorption and saturated absorption signals using our optical system. The saturated absorption signals we have observed were J=0、J=1 and J=2 dips and other three dip of crossover. We check the linewidth, frequency distance of these signal and fitting these signals to make sure that the dips we observed are the helium 2S-3P transitions.
Some related parameters, pressure shift, light shift, and discharge power-dependent experiments, are also analyzed in this thesis. These parameter-dependent experiments can help us optimize signals, enhance S/N ratio.

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