Sensing using differential surface plasmon ellipsometry

Abstract

In this work a differential ellipsometric method utilizing surface plasmons (SPs) for monitoring refractive index changes, which could be used in chemical and biological sensors, is presented. The method is based upon determining the azimuth of elliptically polarized light reflected from a Kretschmann SP system, resulting from linearly polarized light containing both p and s components incident upon it. The sensitivity of this azimuth to the refractive index of a dielectric on the nonprism side of the metal film is demonstrated both experimentally and theoretically. The smallest refractive index change which is resolvable is of the order of 10–7 refractive index units, although it is believed that this could be improved upon were it not for experimental constraints due to atmospheric changes and vibrations. The method requires the Kretschmann configuration to be oriented at a fixed angle, and the SP to be excited at a fixed wavelength. With no moving parts this method would be particularly robust from an application point of view.