FIGURE 3.

Excitation light intensity on the water side of the metal/water (metal) or glass/water (glass) interface as a function of incidence angle θ for p-polarized or s-polarized incident light. Light incident at 0 ≤ θ < θ_c propagates into the water medium, whereas for θ_c ≤ θ < 90° an evanescent field is produced in the water medium. The vertical line marks the θ = θ_c point separating propagating and evanescent. For all incidence angles, the metal severely attenuates s-polarized incident light. Peak transmission for p-polarized light incident on the metal interface occurs at the surface plasmon angle θ_sp. Dielectric constants are ɛ₁ = 1.77, ɛ₂ = −32.5 + i8.4, and ɛ₃ = 2.25 for the water, metal, and glass media, respectively. Metal film thickness is 30 nm and the incident light wavelength is 514.5 nm.