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 m etal grating at certain angles of incidence. The dips appear as dark b ands 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 deri ved from theoretical considerations and is shown to depend on the trac k pitch and the materials involved, but not on the groove depth or wid th. The band locations are confirmed by zeroth order diffraction effic iency measurements as a function of incident angle. A possible negativ e effect of these bands on an optical disk system is the introduction of additional fluctuations and noise into the focusing and push-pull t racking signals.