H3+是由三個質子及二個電子所組成的三原子分子，因為其簡單的結構能夠對於三原子分子系統的理論計算提供一個計算的基礎。目前，H3+在的理論計算準確度約為3 GHz，而在實驗上的頻率準確度約為150 MHz。另一方面，在星際間包含了以氫和各式以氫所組成的分子，對H3+而言，它被認為是星際中含量最為豐富的離子分子。在早期的宇宙中，H3+在冷卻星際環境、並在第一個行星的形成扮演重要的角色。特別的是H3+在星際中與碳和水分子反應，生成碳水化合物，是為生命起源不可或缺的重要成分。而透過高解析的光譜可以提供理論計算更精確的數值，並在未來有機會為量子化學計算、星際反應、行星科學、以及天文觀測上的應用可提供一個發展的平台。

在本論文中，我們建立一套單頻連續波中紅外光並可調的光學光學參量震盪器OPO (cw Mid-IR Optical Parametric Oscillator)。波長連續可調範圍可擴及2.6~4.2μm。利用12 W的幫浦光(1055 -1064 nm)，在3.66 μm附近可輸出之最大功率為900 mW。而產生中紅外的機制主要是利用一塊具氧化鎂摻雜的週期極化反轉铌酸鋰 (Periodically Poled Lithium Niobate; PPLN)作為增益介質，並將幫浦光源利用非線性效應產生signal 光與idler光。在我們實驗中，我們設計一套環形共振腔用以共振signal光進而達到idler光增益的效果。

產生離子的方式則是選用負輝光區延展放電法(Extended Negative Glow Discharge)，負輝光區延展放電法的優點在於輝光強度強、離子濃度高、且在區域中電場效應較小。用來做高解析度光譜是非常好的選擇。

雷射光源的絕對頻率量測則倚靠一套以1.55 μm二極體雷射為中心的光纖鎖模雷射為頻率標準。為了產生超連續光譜用以量測幫浦光源及signal光之頻率，我們利用高非線性光纖將光頻率延展一個八度音(Octave)，涵蓋範圍由1μm~2.2μm，此光頻梳的頻率準確度在1000秒的量測裡達到10-12。同時，我們利用pump-probe的架構來探測H3+的飽和訊號，進而得到數條H3+ν2-band的絕對頻率，其精準度提高到250 kHz。並利用氣壓增寬係數(Pressure Broadening Parameter)得到放電中H3+與氫分子的反應速率，

此外，我們也測量了HeH+的數條譜線。相較於H3+，HeH+則是最簡單的雙原子分子離子，理論計算的準確度也提升到100 MHz以內。在實驗方面以往則得到約60 MHz的準確度。在我們系統中，我們利用飽和吸收光譜法，亦將HeH+的絕對頻率量測準確度相當的準確度，而由於訊躁比不夠，頻率的確定還需未來在改進系統後再加以檢驗。

H3+, consists of three protons and two electrons, is the simplest polyatomic molecule. Due to its simple structure, the theoretical calculation to a very high accuracy can be performed which can also play a role as a benchmark molecule in other calculations for other triatomic species. Currently, the accuracy of theoretical calculation and experimental results can be achieved to be better than 3 GHz and 150 MHz, respectively.

On the other hand, for astronomy, matters consist of hydrogen or its compounds in various forms. For H3+, it is not only the most abundant species in our universe but also exists to be stable at the low temperature and low pressure in the interstellar environments. In the early time of cosmos, H3+ plays a crucial role in cooling down the environment and also in forming the first star. Especially, H3+ interacts with carbon and water and forms carbohydrate which is one of the essential elements of life. Through the technique of high resolution spectroscopy, it is possible to provide a platform to develop or to improve the knowledge of quantum chemical calculations, interstellar chemical reaction, planetary science, and astronomical observation.

In this dissertation, we built up a single frequency, continuous-wave and widely tunable, mid-infrared optical parametric oscillator for our experiments. The frequency tuning range can cover between 2.6~4.2 μm and the output power can be achieved to 900 mW at 12 W pump power (1055 ~ 1064 nm) near 3.66 μm through the nonlinear process of optical parametric generation by a periodically poled lithium-niobate. The pump wave, emitted by an ECDL, was sent into a signal-wave-resonant ring cavity for enhancing the power of idler wave.

The method of producing molecular ions we used is called extended negative glow discharge. The advantages of extended negative glow discharge are its high glow intensity, high concentration of molecular ion and field-free which is beneficial for the application of high resolution spectroscopy.

The absolute frequency measurement of laser source relied on a fiber-based mode-locked laser pumped by 1.55 μm laser diodes. In order to measure the frequency of pump wave and signal wave simultaneously, the spectrum of mode-locked laser was expanded to between 1 μm ~ 2.2 μm (an octave) by a microstructure fiber and the stability can be achieved to be better than 10-12 @ 1000 seconds. On the other hand, for observing the saturation signal of H3+, the experiment was implemented by the pump-probe scheme. We measured several transitions of H3+ in the ν2 fundamental band and the accuracy was 250 kHz. The reaction rate between H3+ and H2 was also acquired by investigating the pressure broadening parameter.

Besides, we also measured several transitions of HeH+ in the fundamental band. HeH+ is the simplest diatomic molecule. The accuracy of theoretical computations and the experimental observations can be achieved to be better than 100 MHz and 60 MHz, respectively. In our system, we also improved the accuracy of frequency measurement of HeH+. However, due to poor signal-to-noise ratio, the absolute frequencies need to be confirmed further after we reform our system.

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