Near-field dynamics at a metallic transmission grating with femtosecond illumination: A theoretical study

Abstract

This paper reports on the temporal and spectral light field evolution for two different types of metallic gratings after illumination with a near-infrared TM-polarized femtosecond pulse: a freestanding grating in air and a grating on a dielectric substrate. The electromagnetic field components are calculated numerically at various transverse locations of the gratings by use of a finite-difference time-domain model. The spectral dynamics are explained by the dynamics of surface plasmon polaritons (SPPs). Fano-like profiles are observed close to an SPP resonance in the calculated spectral curves, indicating a connection between the Rayleigh anomaly and a nearby SPP resonance. For the freestanding grating, only a single Fano-like profile close to the air/metal SPP resonance and, with the dielectric support, two Fano-type profiles are observed, one in the proximity of the air/metal SPP resonance, the other in the proximity of the substrate/metal resonance. Investigating the changes in the spectra for an increasing distance to the grating, it is found that with increasing distance, the spectral curves related to different transverse locations coincide almost completely, providing evidence that the near-field contributions disappeared.