| Abstract: | If the interface between a dielectric surface and an adjacent, fluorescing, medium of lower refractive index is illuminated by a collimated light beam, an exponentially decaying evanescent wave is generated in the fluorescing medium. The electric field of the evanescent wave generates easily measurable fluorescence. If part of the surface is covered with a dielectric film, the fluorescence generated is smaller, since some of the decaying wave occurs in a non-fluorescing medium. Measurement of the difference between the fluorescing signals enables the non-destructive measurement of the film thickness to be made. Several questions arise, for example (i) what angle of incidence should be used, (ii) how is the sensitivity influenced by the substrate refractive index, (iii) should p-or s-polarized light be used, (iv) what sensitivity is attainable? This paper answers these questions and indicates that films of the order of a nanometre in thickness are detectable. |
