Determining the relative permittivity and thickness of a lossless dielectric overlayer on a metal film using optically excited surface plasmon polaritons

Numerical simulations based on the exact Fresnel equations are used to show that it is possible to determine uniquely the relative permittivity and thickness of a thin lossless dielectric film adsorbed on a gold or silver layer. The calculations, which include the effects of up to 1% random noise on the experimental data, show clearly that there is no degeneracy in the solutions of the Fresnel equations even for films as thin as 2 nm. It is shown that gold is preferable to silver as a substrate when the overlayer properties need to be determined accurately. It is further shown that, if the overlayer is bounded by water rather than air,then the experimental constraints would preclude the use of silver as a substrate but measurements would still be possible with gold.