Optimized leaky mode spectroscopy with a single planar film

A transparent dielectric layer coated on a high refractive index prism form s a planar leaky waveguide. The leaky mode spectrum of this layer strongly depends on the imaginary part of the layer refractive index kappa. As an ex ample the leaky mode spectrum of a doped polymer layer is studied theoretic ally and experimentally. For kappa=0 no modes are detectable. In the range of kappa approximate to 10(-4), so-called "optimized leaky modes," can be o bserved while, in the range kappa greater than or equal to 10(-3), broad re sonances with reduced reflectivity can be observed. The imaginary part of t he polymer refractive index was adjusted by doping with the dye malachit gr een with an absorption maximum at lambda=620 nm. (C) 2000 American Institut e of Physics. [S0003-6951(00)01843-X].