Surface Plasmon Lab Report

1.Introduction

1.1 Background:

The phenomenon of surface Plasmon is almost a century old. In 1907, Zenneck formulated a special surface wave solution to Maxwell’s equations and demonstrated theoretically, that radio frequency surface EM wave occur at the boundary of two media when one medium is either a lossy dielectric or a metal, and the other is a loss free medium. Zenneck also suggested that it is the lossy part of dielectric function that is responsible for binding the em wave to the interface. Later Somerfeld found that the field amplitude of the surface wave varied inversely as the square root of the horizontal distances from the source pole. The real progress of the phenomenon of spr was made in 1957, when Ritche theoretically

1.2 Excitation of surface plasmon:

Excitation of surface plasmon waves can be achieved by total internal reflection of p- polarized light waves in prism couplers, optical waveguides, tapered optical fibers etc. a rough surface at which p-polarized light waves are incident, or by using a diffraction grating

a) Excitation of surface plasmons by Attenuated Total Reflection (ATR):

When using light to excite SP waves, there are two configurations which are well known. In the Otto setup, the light illuminates the wall of a glass block, typically a prism, and is totally internally reflected. A thin metal film (for example gold) is positioned close enough to the prism wall so that an evanescent wave can interact with the plasma waves on the surface and hence excite the plasmons. In the Kretschmann configuration, the metal film is evaporated onto the glass block. The light again illuminates the glass block, and an evanescent wave penetrates through the metal film. The plasmons are excited at the outer side of the film. This configuration is used in most practical

A sharp drop in reflected signal is observed at angle өres .

Sensing Principle of SPR: Performance Parameters:

The sensing principle of SPR sensors is based minimum reflectance For a given frequency of the light source and the dielectric constant of metal film one can determine the dielectric constant of the sensing layer adjacent to metal layer by knowing the value of the resonance angle . The resonance angle is determined by using angular interrogation method. The resonance angle is very sensitive to variation in the refractive index (or, dielectric constant) of the sensing layer. Increase in refractive index of the dielectric sensing layer increases the resonance angle. The sensitivity of a SPR sensor with angular interrogation is defined as This simply represents the slope of the reflectivity curve. The above parameter provides primary information regarding the detection sensitivity for SPR sensing