Interaction of polarized light with comb-shaped metal-coated nanostructures

We have studied metal-coated (20-nm-thick gold) periodic grating structures (period $T$ = 350 nm) with a rectangular profile formed on the surface of a GaAs substrate. The spectra of reflection of a linearly polarized light from these gratings have been measured in a wavelength range of 600–1200 nm. A sharp (more than 20-fold) maximum in the polarization contrast has been observed at 720–760 nm. The dependence of this peak on the angle of sample rotation is approximately described by a $\operatorname{cos}^6\theta$ function. The formation of contrast and its features are related to the excitation of surface plasmons at the metal-air interface on vertical walls of the grating structure.