Transmission and scattering properties of subwavelength slits in metals

Using an advanced eigenmode-expansion method, we analyze the basic transmission and scattering properties of subwavelength slits in real metals characterized by the complex optical permittivity ${\ensuremath{\varepsilon}}_{m}$. This includes the slit-width, wavelength, and ${\ensuremath{\varepsilon}}_{m}$ dependences of the efficiencies and cross sections of the main transformation processes: (i) transformation of the incident plane wave into the propagating mode, into the surface plasmons, and into diffracted waves in air and (ii) internal reflection of the propagating mode and its transformation to the surface plasmons and diffracted waves. In conjunction with the known perfect-metal-related efficiencies, the established dependences exhibit a wealth of important subwavelength features, including the nontrivial transmission peculiarities. Transition from the case of the periodic array of slits to the single-slit case when increasing the metal-wall width is considered as well. The established characteristics of a single interface between air and perforated metal are sufficient to describe the extraordinary light transmission through subwavelength slits in metal films.