有机分子第一超极化率色散效应和双光子共振增强理论研究

采用含时Hartree-Fock和多态求和方法计算了半花菁衍生物生色团的第一超极化率色散效应. 采用二能级模型研究了第一超极化率的双光子共振增强特征. 研究发现，第一激发态对半花菁非线性光学性质起决定性作用，随着入射光波长向短波方向移动，二次谐波产生β(-2ω;ω,ω)不断增大并且在950nm附近出现双光子共振效应，理论结果与实验结果较好相符. 此外，共振条件下的二能级模型需要考虑激发态弛豫效应. 研究结果为实验测量和实际应用提供了理论参考. 关键词： 分子非线性光学 超极化率 色散效应 共振增强

Theoretical investigation on dispersion effect and two-photon resonance enhancement of molecular first hyperpolarizability

The calculations of the first hyperpolarizability frequency dispersion effect of hemicyanine derivative chromophore have been performed employing time-dependent Hartree-Fock and sum-over-states method respectively. Two-photon resonance enhancement characteristics of second harmonic generation β(-2ω；ω，ω) have also been investigated using the two-level model (TLM), which was originated by Ouder and Chemla. The results indicate that the first excited state dominates the nonlinear optical properties of hemicyanine derivatives. The first hyperpolarizability β(-2ω；ω，ω) increases with the decrease of fundamental wavelength and gives rise to two-photon resonance near the fundamental wavelength of 950 nm, in accordance with the known experimental facts. In addition, the relaxation effect of the excited states should be considered for TLM in the resonance regime. These researches provide theoretical references for experimental measurements.