Abstract

The fluorescence emission from cyanine dye-arachidic acid monolayers Langmuir-Blodgett deposited onto 1-3 µm poly(styrene) waveguides was investigated. 488-nm light from an argon-ion laser is coupled into the waveguide as a guided mode using high-index LaSF₅ prisms. The evanescent field at the waveguide surface excites the dye fluorescence (emission maximum = 505 nm) which appears superimposed on the Raman spectrum of the poly(styrene) film. The sample size and excitation volume at the polymer surface was varied by increasing the monolayer coverage and through careful mode selection, respectively. Independent variation of these two parameters on the same waveguide provided a method to investigate the evanescent field intensity and effective depth of penetration. Emission spectra demonstrate an intensity increase proportional to the number of monolayers and the concentration of dye molecules. Emission variations due to mode selection are dependent on the number of monolayers and the interfacial amplitude and evanescent decay of the particular mode. We are analyzing the results with multilayer theory calculations and waveguide energy measurements using the Stokes and anti-Stokes Raman peaks of the poly(styrene) waveguide. This method is being developed for biomedical investigations of protein adsorption onto polymer surfaces.

© 1985 Optical Society of America