Simulation of an absorption-based surface-plasmon resonance sensor by means of ellipsometry.

Through numerical simulations, we point out that introduction of an ellipsometric measurement technique to an absorption-based surface-plasmon resonance (SPR) sensor enhances precision and sensitivity in measuring the imaginary part k of the complex refractive index of the sample. By measuring a pair of ellipsometric Delta-Psi parameters, instead of the conventional energy reflectance R(p) of p-polarized light in the Kretschmann optical arrangement, we can detect a small change of k that is proportional to that of the concentration of the sample, especially when k << 1. While one has difficulty in determining the value of k uniquely by the standard technique, when the thickness of Au under the prism is thin (20-30 nm), the ellipsometric technique (ET) overcomes the problem. Furthermore, the value of k and the thickness d(s) of the absorptive sample that is adsorbed on Au can be determined precisely. The ET based on the common-path polarization interferometer is robust against external disturbance such as mechanical vibration and intensity fluctuation of a light source. Although only the p-polarized light is responsible for the SPR phenomenon, we show that the introduction of the ET is significant for quantitative analysis.