氦原子是最簡單的雙電子原子系統，其理論計算與實驗測量皆非常重要，目前已有許多氦原子譜線的躍遷頻率被精密量測。我們計畫量測21S-31D的雙光子躍遷的絕對頻率，並藉由已量測的21S-23S和23S-33D的躍遷頻率得出準確的31D-33D能階差，進一步檢驗理論計算的正確性。
本論文研究使用錐形放大器為增益介質，此錐形放大器的光譜範圍為1000 nm - 1025 nm，並使用Littman-Metcalf架構建立一個波長為1009 nm的外腔式光回饋錐形放大器半導體雷射。初步結果，在波長為1009 nm單頻輸出最大功率為160 mW，閥值電流大約在3300 - 3400 mA左右，效益斜率為0.125 mW/mA，波長可調範圍1002 nm - 1016 nm (~14 nm)，光束剖面圖(Beam profile)為橢圓形並且有高階橫向模態。未來將改善其輸出功率，並以此雷射系統續進行觀測21S-31D的雙光子光譜。

Helium is the simplest two-electron atomic system, and its theoretical calculations and experimental measurements are all very important. Many of atomic helium transitions have been measured, and we plan to measure the absolute frequency of 21S-31D two-photon transition line. This would allow us to obtain highly accurate 31D-33D difference using the precision measured frequencies of 21S-23S, and 23S-33D lines, and further test the correctness of theoretical calculations.
The goal of this thesis is building a 1009 nm external cavity optical feedback tapered amplifier laser, using tapered amplifier which emission spectrum is from 1000 nm to 1025 nm as the gain medium, with Littman-Metcalf configuration. Preliminary results are as follows: maximum output power is 160 mW, single frequency, threshold current around 3300-3400 mA, slope efficiency is 0.125 mW/mA, wavelength tunability is 14 nm, and the beam profile is elliptical with high order transverse mode. We will improve the output power and use this laser as light source to measure 21S-31D transition frequency by two-photon resonance in the future.

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