鐿原子光頻標中泵浦光特性的研究

許朋

鐿原子光頻標中泵浦光特性的研究

許朋

（皖北衛生職業學院，宿州 234000）

鐿原子光頻標中泵浦光參數的優化可以提高鐘頻率穩定度性能。通過分析鐿原子能級分布的特點，建立了能級躍遷速率方程。采用數值計算方法求解速率方程，獲得了泵浦時間與649 nm、770 nm、1388 nm泵浦光的光強和失諧的關系。比較了兩種泵浦方法的效果，分析了泵浦時間的改變對鐘頻率穩定度性能的影響。理論計算的結果為實驗確定泵浦光的光強、泵浦時間提供了重要的參考。

鐿原子光頻標；速率方程；泵浦光

0 引言

1 泵浦方案一分析

圖1 鐿原子的能級圖

649 nm和770 nm泵浦光共同作用下，處于不同能級的原子數的變化方程如下[12-14]

圖3 能級的原子數達到10 000時需要的泵浦時間t隨649 nm和770 nm激光光強的變化

從圖3可知，在649 nm激光光強> 5且770 nm激光光強> 1區域，泵浦時間不超過30 μs。綜合計算的結果，一定條件下，我們取649 nm激光光強= 5，770 nm激光光強= 1。

圖4 能級的原子數達到10 000時需要的泵浦時間t隨激光失諧g和h的變化

圖5 能級的原子數達到10 000時需要的泵浦時間t隨649 nm和770 nm激光失諧的變化

從圖5可知，649 nm激光和770 nm激光的失諧都在-400 MHz以內時，泵浦時間不超過10 ms。一般情況下，649 nm激光的失諧在-200 MHz以內且770 nm激光的失諧在-400 MHz以內時，泵浦時間不超過3 ms。隨著649 nm激光失諧的增大，泵浦時間顯著的變大。

最后分析一下649 nm和770 nm激光頻率漂移引起的泵浦時間的變化d/MHz。假定649 nm和770 nm激光都偏離其對應躍遷的共振頻率200 MHz，在這一點d/MHz的數值為：649 nm為21.9 μs/MHz，770 nm為0.1 μs/MHz。可知，泵浦時間隨649 nm激光頻率漂移變化較大。

2 泵浦方案二分析

圖6 1 388 nm激光作為泵浦光時，鐿原子的能級圖

圖7 能級的原子數達到穩態時需要的泵浦時間t隨1 388 nm激光光強s的變化

從圖8可知，1 388 nm激光失諧從0 MHz增加到-50 MHz時，從0.2 ms增加到21 ms。因此，1 388 nm激光的失諧不能較大，頻率漂移要比較小，否則需要很長的時間才能完成原子的泵浦。

圖8 能級的原子數達到穩態時需要的泵浦時間t隨1 388 nm激光失諧ω的變化

3 討論

4 總結

[1] HUANG Y, GUAN H, LIU P, et al.Frequency comparison of two40Ca optical clocks with an uncertainty at the 10-17level[J]. Physical Review Letters, 2016, 116(1): 013001.

[2] LIN Yi-Ge, WANG Qiang, LI Ye, et al. First evaluation and frequency measurement of the strontium optical lattice clock at NIM[J]. Chinese Physics Letters, 2015, 32(9): 090601

[3] WANG Ye-Bing, YIN Mo-Juan, REN Jie, et al. Strontium optical lattice clock at the National Time Service Center[J]. Chinese Physics B, 2018, 27(2): 208-213.

[4] ZHANG Xiao-hang, ZHOU Min, CHEN Ning, et al. Study on the clock-transition spectrum of cold171Yb ytterbium atoms[J]. Laser Physics Letters, 2015, 12: 025501.

[5] LIU Hui, ZHANG Xi, JIANG Kun-Liang, et al. Realization of closed-loop operation of optical lattice clock based on171Yb[J]. Chinese Physics Letters, 2017, 34(2): 020601.

[6] MCGREW W F,ZHANG X,LEOPARDI H, et al.Towards the optical second:verifying optical clocks at the SI limit[J]. Optica, 2019, 6(4): 448-454.

[7] KOBAYASHI T, AKAMATSU D, HISAI Y, et al. Uncertainty evaluation of an 171Yb optical lattice clock at NMIJ[J]. IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Controlieee Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2018, 65(12): 2449.

[8] NEMITZ N, OHKUBO T, TAKAMOTO M, et al. Frequency ratio of Yb and Sr clocks with 5×10-17uncertainty at 150 s averaging time[J]. arXiv[physics.atom-ph], 2016: 1601.04582.

[9] 張夢嬌. 一維光晶格中鐿原子光頻鐘躍遷譜的研究[D]. 武漢: 中國科學院武漢物理與數學研究所, 2016.

[10] LEE J, LEE J H, NOH J, et al. Core-shell magneto-optical trap for alkaline-earth-metal-like atoms[J]. Physical Review A, 2015, 91(5): 053405.

[11] 梁潔, 賀凌翔.鐿原子激光冷卻的動力學分析[J]. 武漢大學學報(理學版), 2009, 55(6): 665-668.

[12] CHO J W, LEE H, LEE S, et al. Optical repumping of triplet P-states enhances magneto-optical trapping of ytterbium atoms[J]. arXiv[physics.atom-ph], 2011: 1111.6225.

[13] HU F, NOSSKE I, COUTURIER L, et al. Analyzing a single-laser repumping scheme for a strontium magneto-optical trap[J]. arXiv[physics.atom-ph], 2018:1812.01258.

[14] DAMMALAPATI U,NORRIS I, BURROWS C, et al.Spectroscopy and isotope shifts of the 4s3d1D2-4s5p1P1repumping transition in magneto-optically trapped calcium atoms[J]. Physical Review A, 2010, 81: 023424.

[15] 林弋戈,方占軍.鍶原子光晶格鐘[J]. 物理學報, 2018, 67(16): 160601.

The research of the characteristics of pump light in ytterbium atomic optical frequency standard

XU Peng

(North Anhui Health Vocational College, Suzhou 234000, China)

The optimization of the pump light parameters in the ytterbium atomic optical frequency standard can improve the clock frequency stability performance.By analyzing the characteristics of the energy level distribution of ytterbium atom, the energy level transition rate equation was established.The numerical calculation method was used to solve the rate equation, and the relationship between the pumping time and the intensity and detuning of the pump light at 649 nm, 770nm and 1 388 nm was obtained.The effects of the two pumping methods were compared, and the effect of changes in pumping time on the performance of clock frequency stability was analyzed.The results from our theoretical calculation provide an important reference for the experiment to determine the pump light intensity and pumping time.

ytterbium atomic optical frequency standard; rate equation; pump light

10.13875/j.issn.1674-0637.2021-02-0085-07

許朋. 鐿原子光頻標中泵浦光特性的研究[J]. 時間頻率學報, 2021, 44(2): 85-91.

2020-10-15；

2020-12-05