Plasmonic black metal polarizers for ultra-short laser pulses

This paper considers a range of plasmonic-black-metal polarizers suitable for ultra-short pulses. The polarizers consist of a metal surface being nanostructured with a periodic array of ultra-sharp grooves with periods of 250-350 nanometers, and groove depths around 500 nanometers. The surfaces can be designed such that practically all incident light with electric field perpendicular to the groove direction is absorbed. The efficient absorption is due to incident light being coupled into gap-plasmon polaritons that propagate downwards in the gaps between groove walls towards the groove bottom, where it is then subsequently absorbed during propagation. Reflection is largely avoided due to an adiabatic groove taper design. The other polarization, however, is very efficiently reflected, and the main point of this paper is that the reflection is with negligible dispersive stretching even for ultra-short pulses of 5-10 femtoseconds temporal width in the visible and near-infrared. Temporal pulse shapes after reflection are calculated by decomposing the incident laser pulse into its Fourier components, multiplying with the reflection coefficient in the frequency domain, and then Fouriertransforming the product back to the time-domain. Reflection of pulses is compared for polarizers based on different metals (gold, nickel, chromium). Polarizers are studied for two groove-array designs and two directions of light incidence, center wavelengths 650 nm and 800 nm, and pulse widths 5 fs and 10 fs for the incident pulse.