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双光子吸收
Assuming two degenerate photons that are linearly polarized, the TPA cross section (σ$_{TPA}$) can be calculated using the imaginary part of the third-order response property as
精细结构常数α$_f$=e$^2$/(4πε$_0$cħ,其中e电子电荷,ε$_0$真空介电常数,c真空光速,ħ约化普朗克常数
σ$_{TPA}$单位为Göppert-Mayer (1 GM = 10$^{−50}$ cm$^4$ s photon$^{−1}$)
整数N取决于实验设置
γ二阶超极化率,在ADF计算中,超极化率选项选择γ TPA,即可计算γ(-ω,ω,ω,-ω)
ω频率
Im表示取虚部
参考文献
Silverstein, D. W.; Jensen, L. J. Chem. Phys. 2012, 136, 064111.
Beerepoot, M. T. P.; Friese, D. H.; List, N. H.; Kongsted, J.; Ruud, K. Phys. Chem. Chem. Phys. 2015, 17, 19306−19314