Particle Simulation of Resonant Silicon Nanoantennas

Metasurfaces can trap the light at the resonant frequency and enhance the electric field dramatically, which has potential application in energetic electron beam emission, free-electron lasers, etc. Nevertheless, the microscopic picture of electron dynamics is unclear, obscuring an in-depth understanding of the nonlinear optical processes associated.

The plasmonic gold nanorods have been modeled with the particle-in-cell (PIC) simulation, from which the relationship between the microscopic electron kinetics and the plasmon oscillation is revealed. However, PIC simulations in non-metal metasurfaces are more challenging due to photoionization processes. Particularly, to avoid the complicated calculations in Keldysh photoionization theory, the EPOCH (Extendable PIC Open Collaboration) code applies simpler models (i.e., multiphoton and tunneling) in different intensity regimes. Nevertheless, such treatment can lead to considerable error in the transition regime between the two types of ionization. Here, we reduced the computation time significantly and makes high-resolution PIC simulations viable for metasurfaces in the mid-Infrared range. We modeled the electron dynamics in rectangular Si nanoantennas with 200-fs incident laser pulses (peak intensity = 6 - 600 GW/cm²) at λ = 3.6 μm.