Based on Drude-critical points (Drude-Two-CP) model for a dispersive media, a finite-difference time-domain (FDTD) method for metal nanofilms is proposed. By establishing the corresponding relationship between Drude-Two-CP model and Drude–Lorentz model, the conversion coefficients between the two models are calculated. And we modify the Drude-Two-CP model into the form of standard Lorentz model. The transformation relationship between the two models is conducive to the modular programming of FDTD. Formula deduction and calculation results show that Drude-Two-CP model has higher fitting accuracy and fitting formulas are more complex. Using the proposed FDTD method, we have calculated the reflection, transmission and extinction coefficients of gold and aluminium nanofilms. The results show that the FDTD results are in good agreement with those of Drude-Two-CP model, which are better than those of Drude–Lorentz model. Therefore, the Drude-Two-CP-FDTD method proposed in this paper is helpful for improving the accurate modelling and calculation of nano-optical structures.

基于用于分散介质的Drude临界点（Drude-Two-CP）模型，提出了一种用于金属纳米膜的时域有限差分时域（FDTD）方法。通过建立Drude-Two-CP模型和Drude-Lorentz模型之间的对应关系，可以计算两个模型之间的转换系数。然后，我们将Drude-Two-CP模型修改为标准Lorentz模型的形式。两种模型之间的转换关系有利于FDTD的模块化编程。公式推导和计算结果表明，Drude-Two-CP模型拟合精度较高，拟合公式较为复杂。使用提出的FDTD方法，我们计算了金和铝纳米膜的反射，透射和消光系数。结果表明，FDTD结果与Drude-Two-CP模型的结果吻合良好，优于Drude-Lorentz模型。因此，本文提出的Drude-Two-CP-FDTD方法有助于提高纳米光学结构的精确建模和计算效率。