Abstract

The outer surface of a high-performance metal can support a propagating surface wave that decays exponentially into both the metal and the surrounding medium. P-polarized light can be coupled into such a surface wave under conditions involving a narrow range of angles of incidence beyond the critical angle and a correct thickness of metal film, readily achieved by depositing the metal film on the base of a dielectric prism. Illumination of the prism base from within achieves coupling with a surface wave on the outer surface of the metal, characterized by a deep, narrow dip in p-polarized reflectance known as a surface plasmon resonance. Because the resonance depends critically on the conditions at the outer surface of the metal, it is very sensitive to any changes there. In particular, when a very small amount of additional material is added to the metal surface, the resonance responds by moving to a greater angle of incidence and changing its shape. Measurement of these changes can then be interpreted in terms of the properties of the additional layer. Three principal parameters characterize the resonance, width, depth and angular position, and these can be related to the thickness and optical properties of the added layer. This contrasts with ellipsometric measurements that have essentially two parameters and possesses the additional advantage over these and other techniques that the measurement is completely confined to the side of the metal film remote from the film under measurement. The technique has been used in many applications but especially in biochemical investigations of membrane protein processes [1, 2].

© 1998 Optical Society of America