本實驗利用雙光子共振偏極光譜的技術研究銫分子B1Πu態能階要遷譜線的特性。實驗中利用一台鈦藍寶石雷射當作探測光束，以及另外一台外腔二極體雷射當作激發光束，同時作用到裝有銫原子的熱管爐，加溫至235℃讓部分的銫原子化合成銫分子。外腔二極體雷射的頻率固定在12781.400 cm-1使產生B(5, 127)←X(10, 128)的躍遷，而鈦藍寶石雷射頻率則分別在13166.991及13172.280 cm-1附近掃頻探測B(17, 127)←X(10, 128)及B(17, 129)←X(10, 128)的躍遷。在探測光束的路徑上通過熱管爐前後各擺上一偏振片並使其偏振正交，利用兩道雷射光在熱管爐內重合對打作用到同一群的銫分子，若圓偏振激發光束的頻率作用使銫分子產生的躍遷和線性偏振的探測光束所產生的躍遷作用到同一基態X(10, 128)的分子時，則探測光束的偏極方向將發生變化，而有光子能通過另一片振正交的偏振片使得光電倍增管偵測到探測光束。
實驗結果顯示，若固定探測光束的功率在9.9 mW/cm2，而激發光束的功率越高，由0.5 mW/cm2增至250.0 mW/cm2則偵測到的訊號強度越強，但是半高全寬變寬，由30 MHz增至37 MHz。而若固定激發光束的功率在250.0 mW/cm2，改變探測光束的功率時，則在9.9 mW/cm2的半高寬最窄，而功率越高或越低都會使訊號變小而半高全寬變大。改變激發光束的偏振性質由圓偏振光變成橢圓再改變為線性，所偵測到的訊號中兩翼的高度差越來越大，我們也試著計算理論之偏振譜線圖形來和實驗比較。

In this experiment, the double resonance polarization spectroscopy technique was used to study the line shape of the B1Πu state of cesium molecule. Two lasers, a Ti-sapphire laser as probe beam and an external cavity diode laser (ECDL) as pump beam, were used. The laser beams were counter-propagated and overlapped at the center of the heat pipe with cesium molecules at temperature of 235℃. The frequency of ECDL is at 12781.400 cm-1 to excite the transition of B(5, 127)←X(10, 128). The frequency of Ti-sapphire laser is scanned near 13166.991 and 13172.280 cm-1 corresponding to the transitions of B(17, 127)←X(10, 128) and B(5, 129)←X(10, 128), respectively. A polarizer and a Tompson prism were placed with crossed polarization before and after the heat pipe. If the pump and probe beams made transitions with a common ground state of X(10, 128), the polarization of the probe beam will be perturbed so that photon will go through the Tompson prism and can be detected by PMT.
Signal with transmitted at center were observed from the spectrum. The signal received by PMT will be varied with intensity of the pump beam power and the fall width at half maximum(FWHM) of the transmitted center is broadened, from 30MHz to 37MHz, as the intensity of pump beam increased, from 0.5mW/cm2 to 250.0mW/cm2. If we change the probe beam intensity, the FWHM of the transmitted center was obtained at the intensity of the probe beam around 9.9mW/cm2. There will become small in signal and broaden in FWHM when the power is higher or smaller then 9.9mW/cm2. The line shape of the signal was also studied by changing polarization of the pump beam. The polarization spectrum from theoretical prediction was plotted for comparison.

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