精密雷射光譜量測是驗證原子系統理論最有效的方法，而在量子電動力學理論裡，最簡單的三體系統(Three body system) 理論可以藉由測量氦原子光譜來做驗證。我們計劃測量3He 在1009 nm的 21S-31D雙光子躍遷的絕對頻率，配合21S-23S和23S-33D的準確躍遷頻率得出31D-33D的能階差，進一步檢驗理論計算的正確性。
本論文裡，我們首先架設一波長為1009 nm的外腔式二極體雷射(external cavity diode laser, ECDL)，為了增加ECDL的穩定性，我們採用光柵與雷射二極體一體成形的結構。ECDL的電流供應器我們參考John Hall的電路設計，輸出上限為212 mA。當溫度控制在18度，輸入電流為178 mA時，ECDL的輸出功率為42 mW。接著將ECDL輸出經過一隔離度為60 dB的光隔離器降低回授光，射入一錐狀放大器(tapered amplifier)，形成一主震盪功率放大器(master oscillator power amplifier, MOPA)。我們的MOPA系統，閥值電流約為1.898 A，效益斜率為0.405 mW/mA，注入電流5.95 A時，輸出功率達1.65 W，功率放大57倍。此雷射頻率飄移量小於26 MHz/min，單模頻率可調範圍(mode hop free range)約為1.9 GHz。

In simple atomic systems, it is powerful and useful method on theoretical examination by laser spectroscopy. The simplest case, which is three-body-system, can be verified by 3He. We plan to measure the absolute frequency of the 21S-31D transition of 3He by two photon absorption and compare to the transition of 21S-23S and 23S-33D to decide the absolute frequency of 31D-33D.
In this paper, we construct and Master Oscillator Power Amplifier (MOPA) laser system. The inject laser is an external cavity diode laser (ECDL) with 1009 nm of the wavelength and 42 mW of the optical power. Preliminary results of the MOPA laser system are as follows: maximum output power of 1.65 W, single frequency, threshold current of 1.898 A, slope efficiency of 0.405 W/A. We will improve the stability and use this laser as light source to measure the transition of 21S-31D by two-photon in the future.

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