直接光梳光譜（direct frequency comb spectroscopy）的研究近期有長足的發展[1]，尤其是亞利桑那光學中心的Jason Jones實驗室[2]以及美國國家標準局(NIST) J. Kitchen[3]實驗室、還有本實驗室[4]利用此技術發展的”光梳雷射光鐘”，其核心概念為以光梳雷射輸出直接激發原子躍遷，再以此躍遷訊號回授穩定雷射的頻率。 本論文將聚焦於穩定在Rubidium 5S-5P-5D階梯式雙光子躍遷(stepwise two-photon transition， STPT)的光梳雷射光鐘，解析STPT直接光梳光譜的特性、解釋單一譜線的形狀，尤其聚焦在研究影響STPT直接光梳光譜的頻率準確度的各種因素，並且提出對應的手段來消除頻率誤差。在所有因素中，light shift是光梳雷射光鐘最主要的頻率誤差來源。對此本論文提出了利用脈衝頻譜整形(pulse spectral shaping)來控制light shift強度的辦法，並結合藉由optical power modulation與lock-in amplifier解調的回授機制，建構了一套可以自動補償light shift的架構。 本論文的研究將給出以下結論：以階梯式雙光子躍遷為基礎的光梳雷射光鐘具備多項優勢，包括其躍遷的激發強度高、不受光梳雷射頻寬影響的譜線線寬與絕對頻率、有消除light shift頻率誤差的可行手段、相對精簡的系統架設、並且可以同時提供從微波到光頻的穩定頻率標準，本研究認為此系統具備成為光鐘（optical clock）的潛力。;Direct frequency comb spectroscopy has made significant progress in recent years [1]， particularly in its application to frequency-comb-based optical clocks， as demonstrated by Jason Jones’s group at the University of Arizona [2]， J. Kitching’s group at NIST [3]， and our laboratory [4]. This thesis focuses on a frequency-comb optical clock， based on a rubidium 5S-5P-5D stepwise two-photon transition (STPT). We analyze the spectral characteristics and lineshape of comb-laser-induced STPT spectroscopy， with a focus on the factors affecting frequency accuracy and the corresponding methods to suppress frequency errors. Among these factors， the light shift is the primary source of frequency error in comb-laser-based optical clocks. To address this issue， we propose a method for controlling the light shift using pulse spectral shaping. In addition， by incorporating a feedback mechanism based on optical power modulation and lock-in amplifier demodulation， we construct a scheme capable of automatically compensating the light shift. Our results show that the STPT-based comb clock provides several advantages， including high excitation efficiency， effective light-shift cancellation， a relatively simple setup， and the ability to provide frequency references from microwave to optical frequencies. These features make the system a promising candidate for being an optical clock.
