Phase shift detection of surface plasmon using spectral ellipsometer

The phase change caused by excitation of surface plasmons (SP) in a Kretschmann configuration was measured by a rotating polarizer scheme using commercial spectral ellipsometer (GES5, SOPRA, Co). The setup was used to determinate the optical constants at 800 nm of an octadecanthiol (ODT) with a thickness of 9 nm on a gold film. The numerical values n=0.18, k=3.44 for the Au film, and n=1.4 for ODT were obtained by a best-fit procedure to experimental data. From model calculations it is argued that in thin-film cases SP phase measurements give more precise values for the optical constants than conventional ellipsometry and SP amplitude methods. Combination of SP method with advantages of phase measurements of ellipsometry showed sufficient increase in sensitivity (more than one order of magnitude). This methodology could be used for detection of monolayer and even submonolayer films on metals.