Effect of surface plasmon excitations on the irradiance pattern of the return beam in optical disk data storage

The excitation of surface plasmons at a dielectric-metal interface is responsible for dips in the zeroth order diffraction efficiency of a metal grating at certain angles of incidence. The dips appear as dark bands in the returning irradiance pattern in an optical disk system and are seen only when there is a component of incident polarization that lies perpendicular to the tracks. The location of these bands is derived from theoretical considerations and is shown to depend on the track pitch and the materials involved, but not on the groove depth or width. The band locations are confirmed by zeroth order diffraction efficiency measurements as a function of incident angle. A possible negative effect of these bands on an optical disk system is the introduction of additional fluctuations and noise into the focusing and push-pull tracking signals.