A theory for the $s$-polarized optical properties of a metallic slab of arbitrary thickness is presented. The light can be incident upon the slab at an arbitrary angle of incidence, and it is assumed that the surface electron scattering is diffuse. Intersecting oscillatory structure appears in the absorptance for a thin film when the frequency is in the range $0.01{\omega }_p-0.1\mathrm{}{\omega }_p$, where ${\omega }_p$ is the plasma frequency. The origin of this structure is discussed. An expression is derived for the absorptance of a thick sample in the infrared.

• Received 27 April 1970

DOI:https://doi.org/10.1103/PhysRevB.2.2923