A Drude-Two-CP-FDTD method for Drude-critical points model of metal nanofilms

Abstract

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.