本實驗主要是測量12C16O2在4.3 μm附近0111←0110熱頻帶(hot band)躍遷譜線的絕對頻率，目的是為了提供最準確的譜線躍遷頻率作為理論計算與模擬的基礎。我們將實驗數據結合分子常數擬合公式，可以得到新的分子常數預測二氧化碳頻率的參考。

實驗系統光源為窄線寬且波長可調之中紅外差頻雷射光，此差頻光源是利用鈦藍寶石雷射(Ti:Sapphire laser)與釹釔鋁石榴雷射(Nd:YAG laser)通過週期性反轉非線性晶體，產生波長2.6~4.7 μm的中紅外光源。利用此中紅外光源從事飽和吸收光譜的研究，並測量躍遷譜線的絕對頻率，頻率測量的方法是將Nd:YAG 雷射鎖在127 I2 R(56)32-0, a10標準譜線上作雷射穩頻，並將Ti:Sapphire雷射鎖在譜線三階微分訊號的中心，最後用光頻梳系統(OFC)來測得此時Ti:Sapphire雷射精確頻率，並計算得到飽和吸收線的絕對頻率。

首先，我們利用測量標準譜線CH4 F2(2) P(7)的絕對頻率來測試及分析我們的實驗系統。在良好的光模態與準相位匹配下，可以產生光功率約5 mW以上波長3.39 μm的中紅外差頻光，其光產生效率約為理論計算值的43 %。飽和譜線訊噪比約為200且鎖頻後的標準差為5 kHz，測量到的躍遷譜線中心頻率不準度為15 kHz，與標準譜線數據之中心頻率相差30 kHz。

12C16O2 0111←0110躍遷譜線頻率測量實驗中，我們利用加熱二氧化碳氣體，增加在0110振動能階的12C16O2數量，可以得到較強的0111←0110躍遷譜線吸收訊號。利用上述的高解析度的中紅外差頻光源與高精密的光頻梳系統，測量0111←0110 P(30)躍遷譜線的線寬與絕對頻率，其中心頻率為69,267,228.761(15) MHz，每次測得的標準差約為24 kHz。此外，測量在12C16O2 0111←0110 P(30)躍遷譜線頻率± 0.5 GHz內其他二氧化碳之躍遷譜線，當12C16O2 0111←0110 P(30)訊噪比 > 30 dB時，旁邊強度較弱的線的訊噪比可以達到 ~ 10 dB，藉由此次測量，可以瞭解飽和吸收光譜系統的靈敏度與準確度，可以作為未來的實驗方向的參考。

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