Measurement of the concentration of a solution with surface plasmon resonance heterodyne interferometry

A linearly polarized light beam is incident on the boundary surface between the thin metal film of a surface plasmon resonance (SPR) apparatus and the tested solution. If the incident angle is very near to the resonant angle, then the phase difference between p- and s-polarizations of the reflected light is changed with the concentration of the solution. The phase difference can be measured accurately by heterodyne interferometry. Based on these effects, a method for measuring the concentration of a solution is presented. Because the reflected light is measured, only a small quantity of the solution is required. In addition, the method has the advantages of both common-path interferometry and heterodyne interferometry. (C) 2003 Society of Photo-Optical Instrumentation Engineers.