Surface plasma wave applications

Surface plasma waves (SPWs) are electromagnetic oscillations that occur at the interface between a metal and a dielectric medium. The wave amplitude reaches a maximum at the interface and decays exponentially along the normal direction within each medium, with a decaying length on the order of a wavelength. Because SPW excitation is a resonant phenomenon which is strongly dependent on the boundary conditions, SPWs are sensitive probes of optical and structural properties of the interface, allowing, by means of visible light, the detection of changes of sub-angstrom dimensions in thin films covering a metal surface. The resonant nature of the excitation also leads to a wave intensity two to three orders of magnitude higher than the intensity produced by a conventional electromagnetic wave striking a metal surface. Therefore, light scattering from surface irregularities can be enhanced by the same factor under SPW excitation, and structural information can be obtained. Measurement of SPW basic parameters such as amplitude, velocity and damping is achieved using simple optical procedures. These procedures are described and applied in this thesis for the characterization of multilayer rough surfaces and for the simultaneous determination of coating thickness and substrate optical constants of dielectric-coated, metal mirrors. These applications are relevant in the diagnosis of optical and structural properties of thin films. We also use the high sensitivity of SPWs to the presence of very thin coatings to design a surface plasmon immunoassay (SPI) for monitoring immunochemical reactions occurring nearby a metal surface. In particular, the SPI can be used as a simple and rapid procedure to determine antibody levels in blood serum, which is of interest in the field of immunology.