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中国物理学会期刊

激光冷却KCl阴离子的理论研究

CSTR: 32037.14.aps.68.20190869

Theoretical study of laser cooling of potassium chloride anion

CSTR: 32037.14.aps.68.20190869
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  • 本文采用多组态相互作用方法计算了KCl阴离子前两个离解极限K(2Sg) + Cl(1Sg)和K(2Pu) + Cl(1Sg)所对应的3个电子态(X2Σ+, A2Π和B2Σ+)的电子结构. 在计算中考虑了Davidson修正, 核-价电子关联效应及自旋轨道耦合效应. 预测了KCl阴离子的光谱常数和跃迁性质. 计算得到(2)1/2(ν′)↔(1)1/2(ν′′)和(1)3/2(ν′)↔(1)1/2(ν′′) 跃迁具有高对角分布的弗兰克-康登因子, 分别为0.8816和0.8808; 并且(2)1/2和(1)3/2激发态的自发辐射寿命分别为45.7和45.5 ns. 分别利用(2)1/2(ν′)↔(1)1/2(ν′′)和(1)3/2(ν′)↔(1)1/2(ν′′)跃迁构建了准闭合的能级系统, 冷却KCl阴离子所需的主激光波长分别为1065.77和1064.24 nm. 同时预测了激光冷却KCl阴离子能达到的多普勒温度和反冲温度. 计算结果为进一步激光冷却KCl阴离子的实验提供了理论参数.

     

    The potential energy curves and transition dipole moments (TDMs) for three Λ-S states (X2Σ+, A2Π, and B2Σ+) of potassium chloride anion (KCl) are investigated by using multi-reference configuration interaction (MRCI) method. The def2-AQZVPP-JKFI of K atom and AV5Z-DK all-electron basis set of Cl atom are used in all calculations. The Davidson correction, core-valence (CV) correction, and spin-orbit coupling effect (SOC) are also considered. In the complete active self-consistent field (CASSCF) calculations, eight molecular orbitals are selected as active orbitals, which includ K 4s4p and Cl 3s3p shells; K 3p shell is closed orbital, and the remaining shells (K 1s2s3s and Cl 1s2s2p) are frozen orbitals. In the MRCI+Q calculations, K 3p shell is used for the CV correction. There are 15 electrons in the correlation energy calculations. Then, their spectroscopic parameters, Einstein coefficients, Franck-Condon factors, and radiative lifetimes are obtained by solving the radial Schrödinger equation. The spectroscopic properties and transition properties for the Ω states are predicted. Highly diagonally distributed Franck-Condon factor f00 values for the (2)1/2↔(1)1/2 and (1)3/2↔(1)1/2 transition are 0.8816 and 0.8808, respectively. And the short radiative lifetimes for the (2)1/2 and (1)3/2 excited states are also obtained, i.e. τ(2)1/2 = 45.7 ns and τ(1)3/2 = 45.5 ns, which can ensure laser cooling of KCl anion rapidly. The results indicate that the (2)1/2↔(1)1/2 and (1)3/2↔(1)1/2 quasicycling transitions are suitable to the building of laser cooling projects. For driving the (2)1/2↔(1)1/2 transition, a main pump laser (λ00) and two repumping lasers (λ10 and λ21) are required. Their wavelengths are λ00 = 1065.77 nm, λ10 = 1090.13 nm and λ21 = 1087.76 nm. For driving the (1)3/2↔(1)1/2 transition, the wavelengths are λ00 = 1064.24 nm, λ10 = 1088.54 nm, and λ21 = 1086.17 nm. The cooling wavelengths of KCl- anion for two transitions are both deep in the infrared range. Finally, the Doppler temperature and recoil temperature for two transitions are also calculated, respectively. The Doppler temperatures for (2)1/2↔(1)1/2 and (1)3/2(1)1/2 transitions are 83.57 μK and 83.93 μK, and the recoil temperatures for two transitions are 226 nK and 227 nK, respectively. for two transitions are 226 nK and 227 nK, respectively.

     

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