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原子法激光同位素分离的核心之一是如何高效地将原子激发电离.本文从原子法激光同位素分离的实际情况出发，研究了原子吸收谱线的Doppler展宽对原子电离率的影响.研究中使用的理论工具是原子激发电离的密度矩阵方程，并利用数值计算方法对方程进行求解.研究结果表明：当吸收谱线有Doppler展宽时，在激光参数不变的条件下原子电离率会降低；且当激光功率固定时，存在使原子电离率为最大的线宽值.这与已发表文献中无Doppler展宽时的计算结果有很大不同.为了追求最佳的原子电离效果，在原子法激光同位素分离系统中激光应该尽可能地工作在最佳线宽条件下.如果激光线宽有不可控的随机波动，在技术上让激光线宽略大于最佳线宽更为有利.无论如何控制激光线宽，尽可能地降低原子吸收谱线的Doppler展宽都有利于原子电离率的提高.Photoexcitation and photoionization of atoms, the central part of atom vapor laser isotope separation (AVLIS), relate to the ionization yield and isotope selectivity directly. Doppler broadening of absorption lines is one of the parameters that influence the photoexcitation and photoionization process of atoms. When evaporation temperature is high or beam equipment is absent, Doppler broadening has obvious influence on the ionization yield because most of atoms are non-resonantly excited. In this paper, we study the influences of Doppler broadening of absorption lines on a multi-step photoexcitation and photoionization process of atoms according to the facts of AVLIS. A Doppler-broadened three-level atom system with two resonant lasers is investigated. The interaction between laser field and atoms is described by a density matrix, which is calculated by fourth-order Runge-Kutta numerical method with variable steps. The results show that the ionization yield of atoms decreases with the increase of Doppler broadening of absorption lines under the same laser parameters. At a constant laser power, the ionization yield reaches its maximum value at the best laser bandwidths, which is different from that obtained without Doppler broadening, as reported in published papers. Meanwhile, the best laser bandwidth increases with the increase of Rabi frequency and Doppler broadening when other parameters are constant. Moreover, the best bandwidth of the second laser is smaller than that of the first laser in a multi-step photoionization process of atoms. Therefore, lasers should work at the best bandwidths in AVLIS for highest ionization yield. It is advantageous to make laser bandwidths slightly bigger than the best bandwidths technically for smaller fluctuation of ionization yield, owing to incoercible stochastic volatility in laser bandwidths. The ionization yield increases with the decrease of Doppler broadening, especially at the best laser bandwidths. Therefore, it is necessary to reduce Doppler broadening of atom vapor in laser ionization zone.
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Keywords:
- Doppler broadening /
- laser bandwidth /
- Rabi frequency /
- ionization yield
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[2] Xie S L, Wang D W, Ying C T 1997 Chin. J. Nucl. Sci. Eng. 17 166 (in Chinese)[谢世亮, 王德武, 应纯同 1997 核科学与工程 17 166]
[3] Fan F Y, Wang L J 2011 Acta Phys. Sin. 60 093203 (in Chinese)[范凤英, 王立军 2011 60 093203]
[4] Zoller P, Lambropoulos P 1980 J. Phys. B:Atom. Molec. Phys. 13 69
[5] Choe A S, Rhee Y, Lee J, Kuzmina M A, Mishin V A 1995 J. Phys. B:At. Mol. Opt. Phys. 28 3805
[6] Zoller P 1979 Phys. Rev. A 19 1151
[7] Qi X Q, Wang F, Dai C J 2015 Acta Phys. Sin. 64 133201 (in Chinese)[戚晓秋, 汪峰, 戴长建 2015 64 133201]
[8] Agostini P, Georges A T, Wheatley S E, Lambropoulos P, Levenson M D 1978 J. Phys. B:Atom. Molec. Phys. 11 1733
[9] Dai B N, Lambropoulos P 1986 Phys. Rev. A 34 3954
[10] Olivares I E, Duarte A E, Saravia E A, Duarte F J 2002 Appl. Opt. 41 2973
[11] Saleem M, Hussain S, Rafiq M, Baig M A 2006 J. Appl. Phys. 100 053111
[12] Jana B, Majumder A, Kathar P T, Das A K 2011 Appl. Phys. B 102 841
[13] Brinkmann U, Hartig W, Telle H, Walther H 1974 Appl. Phys. 5 109
[14] Li Z M, Zhu F R, Deng H, Zhang Z B, Ren X J, Zhai L H, Wei G Y, Zhang L X 2002 J. Atom. Mol. Phys. 19 383 (in Chinese)[李志明, 朱凤蓉, 邓虎, 张子斌, 任向军, 翟利华, 韦冠一, 张利兴 2002 原子与分子 19 383]
[15] Demtrder W (translated by Ji Y) 2012 Laser Spectroscopy (Vol. 2:Experimental Techniques) (Beijing:Science Press) pp147-161 (in Chinese)[沃尔夫冈戴姆特瑞德 著 (姬扬 译) 2012 激光光谱学(第2卷:实验技术) (北京:科学出版社) 第147161页]
[16] Sankari M, Kumar P V K, Suryanarayana M V 2006 Opt. Commun. 259 612
[17] Pomerantz A E, Zare R N 2003 Chem. Phys. Lett. 370 515
[18] Zhang G Y, Tao Q Y, Ren Z, Zheng H M 2016 Optik 127 8570
[19] Das R M, Chatterjee S, Iwasaki M, Nakajima T 2015 J. Opt. Soc. Am. B:Opt. Phys. 32 1237
[20] Bo Y, Bao C Y, Zhu Y H, Wang D W, Yu Y H 2000 J. Tsinghua Univ. (Sci. Tech.) 40 16 (in Chinese)[薄湧, 包成玉, 诸渔泓, 王德武, 余耀辉 2000 清华大学学报(自然科学版) 40 16]
[21] Xie G F, Wang D W, Ying C T 2002 J. Tsinghua Univ. (Sci. Tech.) 42 1011 (in Chinese)[谢国锋, 王德武, 应纯同 2002 清华大学学报(自然科学版) 42 1011]
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[1] Wang D W 1999 Theory and Application of Laser Isotope Separation (Beijing:Atomic Energy Press) pp167-170 (in Chinese)[王德武 1999 激光分离同位素理论及其应用(北京:原子能出版社) 第167170页]
[2] Xie S L, Wang D W, Ying C T 1997 Chin. J. Nucl. Sci. Eng. 17 166 (in Chinese)[谢世亮, 王德武, 应纯同 1997 核科学与工程 17 166]
[3] Fan F Y, Wang L J 2011 Acta Phys. Sin. 60 093203 (in Chinese)[范凤英, 王立军 2011 60 093203]
[4] Zoller P, Lambropoulos P 1980 J. Phys. B:Atom. Molec. Phys. 13 69
[5] Choe A S, Rhee Y, Lee J, Kuzmina M A, Mishin V A 1995 J. Phys. B:At. Mol. Opt. Phys. 28 3805
[6] Zoller P 1979 Phys. Rev. A 19 1151
[7] Qi X Q, Wang F, Dai C J 2015 Acta Phys. Sin. 64 133201 (in Chinese)[戚晓秋, 汪峰, 戴长建 2015 64 133201]
[8] Agostini P, Georges A T, Wheatley S E, Lambropoulos P, Levenson M D 1978 J. Phys. B:Atom. Molec. Phys. 11 1733
[9] Dai B N, Lambropoulos P 1986 Phys. Rev. A 34 3954
[10] Olivares I E, Duarte A E, Saravia E A, Duarte F J 2002 Appl. Opt. 41 2973
[11] Saleem M, Hussain S, Rafiq M, Baig M A 2006 J. Appl. Phys. 100 053111
[12] Jana B, Majumder A, Kathar P T, Das A K 2011 Appl. Phys. B 102 841
[13] Brinkmann U, Hartig W, Telle H, Walther H 1974 Appl. Phys. 5 109
[14] Li Z M, Zhu F R, Deng H, Zhang Z B, Ren X J, Zhai L H, Wei G Y, Zhang L X 2002 J. Atom. Mol. Phys. 19 383 (in Chinese)[李志明, 朱凤蓉, 邓虎, 张子斌, 任向军, 翟利华, 韦冠一, 张利兴 2002 原子与分子 19 383]
[15] Demtrder W (translated by Ji Y) 2012 Laser Spectroscopy (Vol. 2:Experimental Techniques) (Beijing:Science Press) pp147-161 (in Chinese)[沃尔夫冈戴姆特瑞德 著 (姬扬 译) 2012 激光光谱学(第2卷:实验技术) (北京:科学出版社) 第147161页]
[16] Sankari M, Kumar P V K, Suryanarayana M V 2006 Opt. Commun. 259 612
[17] Pomerantz A E, Zare R N 2003 Chem. Phys. Lett. 370 515
[18] Zhang G Y, Tao Q Y, Ren Z, Zheng H M 2016 Optik 127 8570
[19] Das R M, Chatterjee S, Iwasaki M, Nakajima T 2015 J. Opt. Soc. Am. B:Opt. Phys. 32 1237
[20] Bo Y, Bao C Y, Zhu Y H, Wang D W, Yu Y H 2000 J. Tsinghua Univ. (Sci. Tech.) 40 16 (in Chinese)[薄湧, 包成玉, 诸渔泓, 王德武, 余耀辉 2000 清华大学学报(自然科学版) 40 16]
[21] Xie G F, Wang D W, Ying C T 2002 J. Tsinghua Univ. (Sci. Tech.) 42 1011 (in Chinese)[谢国锋, 王德武, 应纯同 2002 清华大学学报(自然科学版) 42 1011]
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