利用822.5 nm穩頻雷射探測銫原子6S-8S躍遷譜線並量測其絕對頻率與線寬。透過電光調制器將雷射頻率鎖在銫原子氣室的交叉線上，藉由改變電光調制的訊號頻率進而改變雷射頻率並得到躍遷譜線。量測一處於高真空環境的銫原子氣室其譜線訊號，得到此氣室躍遷絕對頻率及線寬860 kHz。
　　將一玻璃銫原子氣室置於高壓氦氣中，並隨時探測6S-8S躍遷譜線，其線寬增加、躍遷中心頻率藍移。並得到6S-8S躍遷中心頻率偏移量與線寬增加量的比值為0.24。
　　與本研究團隊於2012年所量測的10個銫原子譜線相比對，發現其躍遷中心頻率偏移量與線寬增加量的比值與氦氣影響之值相近。本實驗再測量其中兩個銫原子氣室之譜線，其線寬分別增寬185 kHz及228 kHz，躍遷中心頻率分別增加45.3 kHz及46.8 kHz，其躍遷中心頻率偏移量與線寬增加量的比值與氦氣影響之值接近，因此銫原子氣室很有可能由於氦氣滲透玻璃影響躍遷譜線。

Cesium atom 6S-8S hyperfine transition was observed by 822.5 nm frequency-stabilized laser and its absolute frequency and linewidth were determined. The laser frequency is lock to the crossover line of cesium transition by the electro-optic modulator. The laser frequency is changed by changing the frequency of the electro-optic modulation and the relevant fluorescence is obtained. The ultimate transition frequency and linewidth were determined under a high-vacuum (〖10〗^(-10)Torr) system where the residual gas could be constantly pumped out by an ion-pump.
A cesium glass cell was implemented in 1.75 atm helium gas and the 6S-8S transition line was monitored. The linewidth was increased and the center frequency of transition was blue shifted. The ratio of the center frequency shift with respect to the linewidth broadening of the 6S-8S transition is 0.24.
The value of “0.24” is the same as what we have concluded in 2012 via the observation of 10 cesium cells. We future observed the variation of spectral linewidth and frequency for two cesium cells, namely, cell #2 and cell #5. We found that, from 2012 to 2016, the frequency and linewidth of cell #2 increased with 45.3 kHz and 185 kHz, respectively. The frequency and linewidth of cell #2 increased with 45.3 kHz and 185 kHz, respectively. The ratios of the center frequency shift to the linewidth broadening are also near 0.24, which was strongly suspected as were caused by similar helium diffusion from atmosphere.

[1] C. Y. Cheng, C. M. Wu, G. B. Liao, and W. Y. Cheng, "Cesium 6S1/2→8S1/2 two-photon-transition-stabilized 822.5 nm diode laser", Opt. Lett. 32, 563 (2007).
[2] P. Fendel, S. D. Bergeson, Th. Udem, and T. W. Hänsch, "Two-photon frequency comb spectroscopy of the 6s–8s transition in cesium", Opt. Lett. 32, 701 (2007).
[3] G. Hagel, C. Nesi, L. Jozefowski, C. Schwob, F. Nez, and F. Biraben, "Accurate measurement of the frequency of the 6S–8S two-photon transitions in cesium", Opt. Commun. 160, 1(1999).
[4] K. Sasaki, K. Sugiyama, V. Barychev, and A. Onae, "Two-Photon Spectroscopy of the 6S-8S Transitions in Cesium using an Extended-Cavity Diode Laser", Jpn. J. Appl. Phys., Part 1 39, 5310 (2000).
[5] Y. Y. Chen, T. W. Liu, C. M. Wu, C. C. Lee, C. K. Lee and W. Y. Cheng, "High-resolution 133Cs 6S-6D, 6S-8S two-photon spectroscopy using an intracavity scheme", Opt. Lett. 36, 76 (2011).
[6] C. M. Wu, T. W. Liu, M. H. Wu, R. K. Lee and W. Y. Cheng, "Absolute frequency of cesium 6S-8S 822 nm two-photon transition by a high-resolution scheme", Opt. Lett. 38, 3186 (2013).
[7] 吳建明, "光頻梳雷射系統與銫原子6S-8S雙光子躍遷光譜", 清華大學光電工程研究所博士論文 (2014).
[8] Morzynski P et al., "Absolute frequency measurement of rubidium 5S–7S two-photon transitions", Opt. Lett. 38 4581–4 (2013).
[9] N. D. Zameroski , G. D. Hager , C. J. Erickson , and J. H. Burke , "Absolute frequency measurement of rubidium 5S–7S two-photon transitions", J. Phys. B: At., Mol. Opt. Phys. 47, 225205 (2014).
[10] W.A. Rogers, R.S. Buritz, and D. Alpert, "Diffusion coefficient, solubility, and permeability for helium in glass", J. Appl. Phys., 25 (1954), p. 868.
[11] Wolfgang Demtroder, "Laser Spectroscopy", Springer, Berlin, 2nd ed, 1996, Ch 3.3
[12] H. M. Foley, "The Pressure Broadening of Spectral Lines", Phys. Rev. 69, 616 (1946).
[13] M. Kleinert, M. E. Gold Dahl, and S. Bergeson, "Measurement of the Yb I 1S0−1P1 transition frequency at 399 nm using an optical frequency comb", Phys. Rev. A 94, 052511 (2016).
[14] "Alkali Metal Dispensers",
https://www.saesgetters.com/sites/default/files/AMD%20Brochure_0.pdf
[15] Nicole Allard and John Kielkopf, "The effect of neutral nonresonant collisions on atomic spectral lines", Rev. Mod. Phys. 54, 1103 (1982).
[16] reZonator, http://rezonator.orion-project.org/
[17] Spotlight on Optics 2013,
http://www.opticsinfobase.org/spotlight/summary.cfm?URI=ol-38-16-3186