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Microwave electric fields are measured by using cold Rydberg atoms. We obtain spindle-shaped cold atomic clouds in a magneto-optical trap and then pump the cold atoms to quantum state 5S1/2, F = 2, mF = 2 by using an optical-pump laser. We obtain the Rydberg electromagnetic induction transparency (EIT) spectrum peak with narrow linewidth by the low temperature and small residual Doppler broadening. The results show that the typical EIT linewidth with 16 μK cold atoms is about 460 kHz which is 15 times narrower than that of 7 MHz obtained in the thermal vapor cell. The microwave electric field amplitude is measured by Autler-Townes splitting (EIT-AT splitting) in the cold atoms at frequencies of 9.2, 14.2 and 22.1 GHz, receptively. The results show that there is a good linear relationship between the EIT-AT splitting interval and the microwave electric field amplitude. The lower limit of the microwave electric field amplitude that can be measured in the linear region can reach as low as 222 μV/cm, which is about 22 times larger than the lower limit in the traditional thermal vapor cell about of 5 mV/cm. The improvement of the lower limit by EIT-AT splitting method is roughly proportional to the narrowing EIT line width by cold atom samples. This demonstrates that benefiting from the smaller residual Doppler effect and the narrower EIT linewidth in cold atoms, the cold atom system is more advantageous in the experimental measuring of the weak microwave electric field amplitude by using the EIT-AT splitting method. This is of great benefit to the absolute calibration of very weak microwave electric fields. Furthermore, the lower limit of the microwave electric field amplitude that can be measured is smaller than 1 μV/cm by using the change of transmittance of the prober laser at the EIT resonance, and the corresponding sensitivity can reach 1 μV·cm–1·Hz–1/2. These results demonstrate the advantages of cold atomic sample in microwave electric field measurement and its absolute calibration.
[1] Song Z F, Liu H P, X C Liu, Zhang W F, Zou H Y, Zhang J, Qu J F 2019 Opt. Express 27 8848Google Scholar
[2] Wu B H, Chuang Y W, Chen Y H, Yu J C, Chang M S, Yu I A 2017 Sci. Rep. 7 9726Google Scholar
[3] Zhang L J, Jia Y, Jing M Y, Guo L P, Zhang H, Xiao L T, Jia S T 2019 Laser Phys. 29 035701Google Scholar
[4] Zhou J, Zhang C, Liu Q, You J, Zheng X, Cheng X, Jiang T 2020 Nanophotonics 9 2797Google Scholar
[5] Wang Q, Yu L, Gao H, Chu S, Peng W 2019 Opt. Express 27 35012Google Scholar
[6] Wei Z, Li X, Zhong N, Tan X, Zhang X, Liu H, Meng H, Liang R 2017 Plasmonics 12 641Google Scholar
[7] Bao S X, Zhang H, Zhou J, Zhang L J, Zhao J M, Xiao L T, Jia S T 2016 Phys. Rev. A 94 043822Google Scholar
[8] Zhang L J, Bao S X, Zhang H, Raithel G, Zhao J M, Xiao L T, Jia S T 2018 Opt. Express 26 29931Google Scholar
[9] Xue Y M, Hao L P, Jiao Y C, Han X X, Bai S Y, Zhao J M, Raithel G 2019 Phys. Rev. A 99 053426Google Scholar
[10] Cheng H, Wang H M, Zhang S S, Xin P P, Luo J, Liu H P 2017 Opt. Express 25 33575Google Scholar
[11] Sedlacek J A, Schwettmann A, Kübler H, Low T R, Shaffer J P 2012 Nat. Phys. 8 819Google Scholar
[12] Pritchard J D, Maxwell D, Gauguet A, Weatherill K J, Jones M P A, Adams C S 2010 Phys. Rev. Lett. 105 193603Google Scholar
[13] Fan H, Kumar S, Sedlacek J, Kübler H, Karimkashi S, Shaffer J P 2015 J. Phys. B 48 202001Google Scholar
[14] Artusio-Glimpse A B, Simons M T, Holloway C L, 2021 Phys. Rev. A 103 023704Google Scholar
[15] Jia F D, Liu X B, Mei J, Yu Y H, Zhang H Y, Lin Z Q, Dong H Y, Zhang J, Xie F, Zhong Z P 2021 Phys. Rev. A 103 063113Google Scholar
[16] Jing M, Hu Y, Ma J, Zhang H, Zhang L, Xiao L, Jia S 2020 Nat. Phys. 16 911Google Scholar
[17] Kominis K, Kornack T W, Allred J C, Romalis M V 2003 Nature (London) 422 596Google Scholar
[18] 黄巍, 梁振涛, 杜炎雄, 颜辉, 朱诗亮 2015 物理学报 64 160702Google Scholar
Huang W, Liang Z T, Du Y X, Yan H, Zhu S L 2015 Acta Phys. Sin. 64 160702Google Scholar
[19] 樊佳蓓, 郝丽萍, 白景旭, 焦月春, 赵建明, 贾锁堂 2021 物理学报 70 063201Google Scholar
Fan J B, Hao L P, Bai J X, Jiao Y C, Zhao J M, Jia S T 2021 Acta Phys. Sin. 70 063201Google Scholar
[20] 陈志文, 佘圳跃, 廖开宇, 黄巍, 颜辉, 朱诗亮 2021 物理学报 70 060702Google Scholar
Chen Z W, She Z Y, Liao K Y, Huang W, Yan H, Zhu S L 2021 Acta Phys. Sin. 70 060702Google Scholar
[21] 樊佳蓓, 焦月春, 郝丽萍, 薛咏梅, 赵建明, 贾锁堂 2018 物理学报 67 093201Google Scholar
Fan J B, Jiao Y C, Hao L P, Xue Y M, Zhao J M, Jia S T 2018 Acta Phys. Sin. 67 093201Google Scholar
[22] 焦月春, 赵建明, 贾锁堂 2018 物理学报 67 073201Google Scholar
Jiao Y C, Zhao J M, Jia S T 2018 Acta Phys. Sin. 67 073201Google Scholar
[23] 刘强, 何军, 王军民 2021 物理学报 70 163202Google Scholar
Liu Q, He J, Wang J M 2021 Acta Phys. Sin. 70 163202Google Scholar
[24] 裴栋梁, 何军, 王杰英, 王家超, 王军民 2017 物理学报 66 193701Google Scholar
Pei D L, He J, Wang J Y, Wang J C, Wang J M 2017 Acta Phys. Sin. 66 193701Google Scholar
[25] 薛咏梅, 郝丽萍, 焦月春, 韩小萱, 白素英, 赵建明, 贾锁堂 2017 物理学报 66 213201Google Scholar
Xue Y M, Hao L P, Jiao Y C, Han X X, Bai S Y, Zhao J M, Jia S T 2017 Acta Phys. Sin. 66 213201Google Scholar
[26] 薛咏梅, 郝丽萍, 焦月春, 韩小萱, 白素英, 赵建明, 贾锁堂 2017 物理学报 66 243201Google Scholar
Yan L Y, Liu J S, Zhang H, Zhang L J, Xiao L T, Jia S T 2017 Acta Phys. Sin. 66 243201Google Scholar
[27] Fan J B, He Y H, Jiao Y C, Hao L P, Zhao J M, Jia S T 2021 Chin. Phys. B 30 034207Google Scholar
[28] Hao L P, Xue Y M, Fan J B, Bai J X, Jiao Y C, Zhao J M 2020 Chin. Phys. B 29 033201Google Scholar
[29] Hao L P, Xue Y M, Fan J B, Jiao Y C, Zhao J M, Jia S T 2019 Chin. Phys. B 28 053202Google Scholar
[30] Hu L, Hu X M, Hu Q P 2021 Chin. Phys. B 30 064211Google Scholar
[31] Liu X B, Jia F D, Zhang H Y, Mei J, Liang W C, Zhou F, Yu Y H, Liu Y, Zhang J, Xie F, Zhong Z P 2022 Chin. Phys. B 31 090703Google Scholar
[32] Wu X L, Liang X H, Tian Y Q, Yang F, Chen C, Liu Y C, Tey M K, You L 2021 Chin. Phys. B 30 020305Google Scholar
[33] Zhai S Y, Wu J H 2021 Chin. Phys. B 30 074206Google Scholar
[34] Zhang L J, Liu J S, Jia Y, Zhang H, Song Z F, Jia S T 2018 Chin. Phys. B 27 033201Google Scholar
[35] Ahmed E, Lyyra A M 2007 Phys. Rev. A 76 053407Google Scholar
[36] Holloway C L, Simons M T, Gordon J A, Dienstfrey A, Anderson D A, Raithel G 2017 J. Appl. Phys. 121 233106Google Scholar
[37] Gordon J A, Holloway C L, Andrew S, Anderson D A, Miller S, Thaicharoen N, and Raithel G, 2014 Appl. Phys. Lett. 105 024104Google Scholar
[38] Holloway C L, Gordon J A, Andrew S, David A A, Miller S A, Thaicharoen N, Raithel G 2014 Appl. Phys. Lett. 104 244102Google Scholar
[39] Simons M T, Gordon J A, Holloway C L, Anderson D A, Miller S A, Raithel G 2016 Appl. Phys. Lett. 108 174101Google Scholar
[40] Liu X B, Jia F D, Zhang H Y, Mei J, Yu Y H, Liang W C, Zhang J, Xie F, Zhong Z P 2021 AIP Adv. 11 085127Google Scholar
[41] Simons M T, Artusio-Glimpse A B, Holloway C L, Imhof E, Jefferts S R, Wyllie R, Sawyer B C, Walker T G 2021 Phys. Rev. A 104 032824Google Scholar
[42] Zhou F, Jia F D, Mei J, Liu X B, Zhang H Y, Yu Y H, Liang W C, Qin J W, Zhang J, Xie F, Zhong Z P 2022 J. Phys. B:At. Mol. Opt. Phys. 55 075501Google Scholar
[43] Liao K Y, Tu H T, Yang S Z, Chen C J, Liu X H, Liang J, Zhang X D, Yan H, Zhu S L 2020 Phys. Rev. A 101 053432Google Scholar
[44] Tanasittikosol M, Pritchard J D, Maxwell D, Gauguet A, Weatherill K J, Potvliege R M, Adams C S 2011 J. Phys. B 44 184020Google Scholar
[45] Ji Z, Jiao Y, Xue Y, Hao L, Zhao J, Jia S 2021 Opt. Express 29 11406
[46] Jia F D, Yu Y H, Liu X B, Zhang Xi, Zhang L, Wang F, Mei J, Zhang J, Xie F, Zhong Z P 2020 Appl. Opt. 59 2108Google Scholar
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图 1 冷原子里德堡EIT的实验装置示意图. 一对方形梯度磁场线圈和三对MOT冷却光/再泵浦光将原子囚禁成一个长条形的冷原子云. 一对亥姆霍兹线圈(Bias 线圈)提供一个与冷原子云长轴方向平行的均匀弱磁场, 作为量子化轴. 探测光和耦合光相对传输, 并调整到与冷原子云长轴重合, 实验中利用1/4玻片将探测光和耦合光的偏振分别调节为σ+ 和σ –.
Figure 1. Scheme of the cold Atom Rydberg EIT-AT experiments. A pair of square gradient magnetic field coils and three pairs of MOT light are used to cool and trap a cigar-shaped atom cloud. The Bias coil is used to provide a uniform weak magnetic field parallel to the long axis of the elongated cold atom cloud as the quantization axis. In the experiment, a 1/4 wave plate is used to change the polarization of the probe laser and coupling laser into σ+ and σ–.
图 3 本文进行微波测量所用到的能级图 (a) 微波频率为14.2 GHz时的能级图 (b) 微波频率为9.2 GHz时的能级图 (c) 微波频率为22. 1 GHz时的能级图
Figure 3. Atomic energy level schemes of microwave measurements: (a) Atomic energy level scheme for microwave frequency at 14.2 GHz; (b) atomic energy level scheme of for microwave frequency at 9.2 GHz; (c) atomic energy level scheme of for microwave frequency at 22.1 GHz.
图 4 冷原子中典型的EIT-AT分裂光谱. 图中的黄色、紫色、绿色、蓝色、红色和黑色曲线自上而下分别代表微波电场强度为0.007, 0.558, 1.114, 2.222, 3.523和5.583 mV/cm 时的测量结果. 冷原子实验中探测光的强度和光斑直径为500 nW和100 μm, 耦合光强度和光斑直径为60 mW和300 μm.
Figure 4. Examples EIT-AT splitting spectra obtained in cold atoms with different microwave intensities. The yellow, purple, green, blue, red and black curves in the figure represent the measurement results when the microwave electric field intensity is 0.007, 0.558, 1.114, 2.222, 3.523 and 5.583 mV /cm, respectively. In the cold atom experiment, the power and diameter of the probe laser are 500 nW and 100 μm, respectively, the power and diameter of the coupling laser are 60 mW and 300 μm, respectively.
图 5 微波频率为14.2 GHz时, 冷原子和热原子EIT-AT分裂测量结果的比较. 图中蓝色方框代表冷原子测量结果, 红色圆圈代表热原子测量结果. 具体实验参数如下: 冷原子实验中探测光的强度和光斑直径分别为500 nW和100 μm, 耦合光强度和光斑直径分别为60 mW和300 μm. 热原子实验中探测光的强度和光斑直径分别为60 μW和800 μm, 耦合光强度和光斑直径分别为40 mW 和900 μm. 热原子实验数据来自[15]
Figure 5. Comparison of EIT-AT splitting measurements results in cold and thermal atoms samples at microwave frequency of 14.2 GHz. The blue boxes represent the results in cold atomic sample and the red circles represent the results in hot atomic sample. The experimental parameters are as follows: In the cold atom experiment, the power and diameter of the probe laser are 500 nW and 100 μm, the power and diameter of the coupling laser are 60 mW and 300 μm; In the thermal atom experiment, the power and diameter of the probe laser are 60 μW and 800 μm, the power and diameter of the coupling laser are 40 mW and 900 μm. The data of the thermal atom experiment are taken from[15].
图 6 9.2 GHz的微波测量结果 (a) 通过EIT-AT分裂测量的结果, 蓝色方框代表实验结果, 测量线性区的下限可以到 (300±30) μV/cm. 红色实线代表线性公式(1)式的计算结果; (b) 通过EIT透明峰的探测光透过率测量的结果, 蓝色方框代表实验结果, 红色实线代表四能级模型结合多普勒效应的数值计算结果[42]. 测量下限可以到(656±60 n) V/cm
Figure 6. Microwave measurement results at 9.2 GHz by cold atoms: (a) Results measured by the EIT-AT splitting, the blue boxes represent the experimental results, the lower limit of the measurement linear region can achieve (300±30) μV/cm. The solid red line represents the calculation results of Eq. (1). (b) The measured results of the transmittance of the probe laser of the EIT peak. The blue boxes represent the experimental results and the red solid line represents the numerical calculation results of the four-level model combined with the Doppler effect [42]. The lower measurement limit can be achieved as (656±60) nV/cm.
图 7 22.1 GHz的微波测量结果 (a) 通过EIT-AT分裂测量的结果, 蓝色方框代表实验结果, 线性区的下限可以测到 (312±20) μV/cm. 红色实线代表线性公式(1)的计算结果; (b) 通过探测光的透过率测量的结果, 蓝色方框代表实验结果, 红色实线代表四能级模型结合多普勒效应的数值计算结果, 测量的下限可以到 (297±21) nV/cm, 相应的灵敏度可达到1 μV·cm–1·Hz–1/2
Figure 7. Microwave measurement results at 22.1 GHz by cold atoms: (a) Results measured by the EIT-AT splitting, the blue boxes represent the experimental results, the lower limit of the measurement linear region can achieve (312±20) μV/cm. The solid red line represents the calculation results of Eq. (1). (b) The measured results of the transmittance of the probe laser of the EIT transparency peak. The blue boxes represent the experimental results and the red solid line represents the numerical calculation results of the four-level model combined with the Doppler effect [42]. The lower measurement limit can be achieved (297±21) nV/cm. The corresponding sensitivity can reach 1 μV·cm–1·Hz–1/2.
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[1] Song Z F, Liu H P, X C Liu, Zhang W F, Zou H Y, Zhang J, Qu J F 2019 Opt. Express 27 8848Google Scholar
[2] Wu B H, Chuang Y W, Chen Y H, Yu J C, Chang M S, Yu I A 2017 Sci. Rep. 7 9726Google Scholar
[3] Zhang L J, Jia Y, Jing M Y, Guo L P, Zhang H, Xiao L T, Jia S T 2019 Laser Phys. 29 035701Google Scholar
[4] Zhou J, Zhang C, Liu Q, You J, Zheng X, Cheng X, Jiang T 2020 Nanophotonics 9 2797Google Scholar
[5] Wang Q, Yu L, Gao H, Chu S, Peng W 2019 Opt. Express 27 35012Google Scholar
[6] Wei Z, Li X, Zhong N, Tan X, Zhang X, Liu H, Meng H, Liang R 2017 Plasmonics 12 641Google Scholar
[7] Bao S X, Zhang H, Zhou J, Zhang L J, Zhao J M, Xiao L T, Jia S T 2016 Phys. Rev. A 94 043822Google Scholar
[8] Zhang L J, Bao S X, Zhang H, Raithel G, Zhao J M, Xiao L T, Jia S T 2018 Opt. Express 26 29931Google Scholar
[9] Xue Y M, Hao L P, Jiao Y C, Han X X, Bai S Y, Zhao J M, Raithel G 2019 Phys. Rev. A 99 053426Google Scholar
[10] Cheng H, Wang H M, Zhang S S, Xin P P, Luo J, Liu H P 2017 Opt. Express 25 33575Google Scholar
[11] Sedlacek J A, Schwettmann A, Kübler H, Low T R, Shaffer J P 2012 Nat. Phys. 8 819Google Scholar
[12] Pritchard J D, Maxwell D, Gauguet A, Weatherill K J, Jones M P A, Adams C S 2010 Phys. Rev. Lett. 105 193603Google Scholar
[13] Fan H, Kumar S, Sedlacek J, Kübler H, Karimkashi S, Shaffer J P 2015 J. Phys. B 48 202001Google Scholar
[14] Artusio-Glimpse A B, Simons M T, Holloway C L, 2021 Phys. Rev. A 103 023704Google Scholar
[15] Jia F D, Liu X B, Mei J, Yu Y H, Zhang H Y, Lin Z Q, Dong H Y, Zhang J, Xie F, Zhong Z P 2021 Phys. Rev. A 103 063113Google Scholar
[16] Jing M, Hu Y, Ma J, Zhang H, Zhang L, Xiao L, Jia S 2020 Nat. Phys. 16 911Google Scholar
[17] Kominis K, Kornack T W, Allred J C, Romalis M V 2003 Nature (London) 422 596Google Scholar
[18] 黄巍, 梁振涛, 杜炎雄, 颜辉, 朱诗亮 2015 物理学报 64 160702Google Scholar
Huang W, Liang Z T, Du Y X, Yan H, Zhu S L 2015 Acta Phys. Sin. 64 160702Google Scholar
[19] 樊佳蓓, 郝丽萍, 白景旭, 焦月春, 赵建明, 贾锁堂 2021 物理学报 70 063201Google Scholar
Fan J B, Hao L P, Bai J X, Jiao Y C, Zhao J M, Jia S T 2021 Acta Phys. Sin. 70 063201Google Scholar
[20] 陈志文, 佘圳跃, 廖开宇, 黄巍, 颜辉, 朱诗亮 2021 物理学报 70 060702Google Scholar
Chen Z W, She Z Y, Liao K Y, Huang W, Yan H, Zhu S L 2021 Acta Phys. Sin. 70 060702Google Scholar
[21] 樊佳蓓, 焦月春, 郝丽萍, 薛咏梅, 赵建明, 贾锁堂 2018 物理学报 67 093201Google Scholar
Fan J B, Jiao Y C, Hao L P, Xue Y M, Zhao J M, Jia S T 2018 Acta Phys. Sin. 67 093201Google Scholar
[22] 焦月春, 赵建明, 贾锁堂 2018 物理学报 67 073201Google Scholar
Jiao Y C, Zhao J M, Jia S T 2018 Acta Phys. Sin. 67 073201Google Scholar
[23] 刘强, 何军, 王军民 2021 物理学报 70 163202Google Scholar
Liu Q, He J, Wang J M 2021 Acta Phys. Sin. 70 163202Google Scholar
[24] 裴栋梁, 何军, 王杰英, 王家超, 王军民 2017 物理学报 66 193701Google Scholar
Pei D L, He J, Wang J Y, Wang J C, Wang J M 2017 Acta Phys. Sin. 66 193701Google Scholar
[25] 薛咏梅, 郝丽萍, 焦月春, 韩小萱, 白素英, 赵建明, 贾锁堂 2017 物理学报 66 213201Google Scholar
Xue Y M, Hao L P, Jiao Y C, Han X X, Bai S Y, Zhao J M, Jia S T 2017 Acta Phys. Sin. 66 213201Google Scholar
[26] 薛咏梅, 郝丽萍, 焦月春, 韩小萱, 白素英, 赵建明, 贾锁堂 2017 物理学报 66 243201Google Scholar
Yan L Y, Liu J S, Zhang H, Zhang L J, Xiao L T, Jia S T 2017 Acta Phys. Sin. 66 243201Google Scholar
[27] Fan J B, He Y H, Jiao Y C, Hao L P, Zhao J M, Jia S T 2021 Chin. Phys. B 30 034207Google Scholar
[28] Hao L P, Xue Y M, Fan J B, Bai J X, Jiao Y C, Zhao J M 2020 Chin. Phys. B 29 033201Google Scholar
[29] Hao L P, Xue Y M, Fan J B, Jiao Y C, Zhao J M, Jia S T 2019 Chin. Phys. B 28 053202Google Scholar
[30] Hu L, Hu X M, Hu Q P 2021 Chin. Phys. B 30 064211Google Scholar
[31] Liu X B, Jia F D, Zhang H Y, Mei J, Liang W C, Zhou F, Yu Y H, Liu Y, Zhang J, Xie F, Zhong Z P 2022 Chin. Phys. B 31 090703Google Scholar
[32] Wu X L, Liang X H, Tian Y Q, Yang F, Chen C, Liu Y C, Tey M K, You L 2021 Chin. Phys. B 30 020305Google Scholar
[33] Zhai S Y, Wu J H 2021 Chin. Phys. B 30 074206Google Scholar
[34] Zhang L J, Liu J S, Jia Y, Zhang H, Song Z F, Jia S T 2018 Chin. Phys. B 27 033201Google Scholar
[35] Ahmed E, Lyyra A M 2007 Phys. Rev. A 76 053407Google Scholar
[36] Holloway C L, Simons M T, Gordon J A, Dienstfrey A, Anderson D A, Raithel G 2017 J. Appl. Phys. 121 233106Google Scholar
[37] Gordon J A, Holloway C L, Andrew S, Anderson D A, Miller S, Thaicharoen N, and Raithel G, 2014 Appl. Phys. Lett. 105 024104Google Scholar
[38] Holloway C L, Gordon J A, Andrew S, David A A, Miller S A, Thaicharoen N, Raithel G 2014 Appl. Phys. Lett. 104 244102Google Scholar
[39] Simons M T, Gordon J A, Holloway C L, Anderson D A, Miller S A, Raithel G 2016 Appl. Phys. Lett. 108 174101Google Scholar
[40] Liu X B, Jia F D, Zhang H Y, Mei J, Yu Y H, Liang W C, Zhang J, Xie F, Zhong Z P 2021 AIP Adv. 11 085127Google Scholar
[41] Simons M T, Artusio-Glimpse A B, Holloway C L, Imhof E, Jefferts S R, Wyllie R, Sawyer B C, Walker T G 2021 Phys. Rev. A 104 032824Google Scholar
[42] Zhou F, Jia F D, Mei J, Liu X B, Zhang H Y, Yu Y H, Liang W C, Qin J W, Zhang J, Xie F, Zhong Z P 2022 J. Phys. B:At. Mol. Opt. Phys. 55 075501Google Scholar
[43] Liao K Y, Tu H T, Yang S Z, Chen C J, Liu X H, Liang J, Zhang X D, Yan H, Zhu S L 2020 Phys. Rev. A 101 053432Google Scholar
[44] Tanasittikosol M, Pritchard J D, Maxwell D, Gauguet A, Weatherill K J, Potvliege R M, Adams C S 2011 J. Phys. B 44 184020Google Scholar
[45] Ji Z, Jiao Y, Xue Y, Hao L, Zhao J, Jia S 2021 Opt. Express 29 11406
[46] Jia F D, Yu Y H, Liu X B, Zhang Xi, Zhang L, Wang F, Mei J, Zhang J, Xie F, Zhong Z P 2020 Appl. Opt. 59 2108Google Scholar
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