鋰原子低能階的雷射光譜

Laser Spectroscopy of Low-lying Levels in Atomic Lithium

黃耀欽(Yao-Chin Huang)

指導教授 ： 王立邦

國立清華大學/理學院/物理學系/博士(2017年)

摘要

本論文研究鋰原子低能階的雷射光譜。實驗上，我們分別建立兩套相似的雷射系統，其中一套雷射系統為光譜雷射，其頻率穩定在共焦的法布立-培若（Fabry-Pérot）腔體上，藉由改變腔體長度達到掃描雷射的頻率功能並且可得到鋰原子光譜。另一套雷射系統為參考雷射，此雷射的頻率會鎖在碘分子躍遷譜線。利用光電倍增管偵測雷射誘發的螢光訊號，並且記錄兩套雷射系統之間頻率的差值。

在2P_{1/2}超精細結構分裂及D1同位素偏移實驗上，我們釐清了不同的團隊量測結果的爭議。結論上，鋰-6與鋰-7的第一激發態2P_{1/2}超精細結構分裂分別為26.108(9)百萬赫玆和91.873(5)百萬赫玆與目前的理論計算相符。而同位素偏移大小為10533.800(15)百萬赫玆，結合實驗測量與理論計算的同位素偏移也可計算出鋰-7與鋰-6相對均方根核電荷半徑的大小差值為-0.720(6)費米平方。

為了要檢測理論計算在鋰原子低能階的準確度，我們也測量激發態3P_{1/2}的超精細結構分裂。實驗精準度相較以往的測量提高六點七倍，此外，在決定絕對頻率數值精確度提高三千倍。

關鍵字

鋰原子 ； 超精細結構 ； 外腔式雷射 ； 精密光譜 ； 紫光鐳射

並列摘要

This dissertation studies the low-lying levels of ^{6,7}Li in a well-collimated atomic beam. We have built two laser systems, one of which frequency is stabilized on a confocal Fabry-Perot cavity and scans the lithium spectrum by tuning the cavity length as a spectroscopy laser. Another laser is locked to molecular iodine transition near lithium resonance line as a reference laser. The laser-induced fluorescence signal is detected by a photomultiplier, and
the beat frequency between the spectroscopy laser and the reference laser is recorded.

We have claried that the 2P_{1/2} hyperfine structure splitting and D1 isotope shift for stable ^{6,7}Li disagree with previous experiments. The 2P_{1/2} hyperfine interval are 26.108(9) MHz and 91.873(5) MHz for ^{6}Li and ^{7}Li, respectively. The D1 isotope shift is 10533.800(15) MHz. Combining the measured D1 isotope shift with the calculated energy shift determines the relative squared nuclear charge radius to be -0.720(6) fm^{2}.

In order to test atomic calculations in other low-lying levels, we have also measured the hyperfine splitting of 3P_{1/2} state. Our result improves the precision by a factor of 6.7 compared to previous measurements. Furthermore, the absolute frequency is measured and the precision is three thousand times better than previous results.

並列關鍵字

Lithium ； Hyperfine Splitting ； ECDL ； Spectroscopy ； UV Laser

參考文獻

[1] Z.-C. Yan, W. Nortershauser, and G. W. F. Drake, “High precision atomic theory for Li and Be+: QED shifts and isotope shifts,” Phys. Rev. Lett. 100, 243002 (2008).

[2] M. Puchalski, D. Kedziera, and K. Pachucki, “D1 and D2 lines in 6Li and 7Li including QED effects,” Phys. Rev. A 87, 032503 (2013).

[3] M. Puchalski and K. Pachucki, “Fine and hyperfine splitting of the 2P state in Li and Be+,” Phys. Rev. A 79, 032510 (2009).

[4] V. A. Yerokhin, “Hyperfine structure of Li and Be+,” Phys. Rev. A 78, 012513 (2008).

[5] R. Sanchez, W. Nortershauser, G. Ewald, D. Albers, J. Behr, P. Bricault, B. A. Bushaw, A. Dax, J. Dilling, M. Dombsky, G. W. F. Drake, S. G ̈otte, R. Kirchner, H.- J. Kluge, T. Ku ̈hl, J. Lassen, C. D. P. Levy, M. R. Pearson, E. J. Prime, V. Ryjkov, A. Wojtaszek, Z.-C. Yan, and C. Zimmermann, “Nuclear charge radii of 9,11Li: The influence of halo neutrons,” Phys. Rev. Lett. 96, 033002 (2006).