Demonstration of Reciprocity in the Angular Pattern of Fluorescence Emission Collected from Langmuir-Blodgett Deposited Thin Films

Application of a principle of reciprocity results in an explicit prediction for the angular pattern of fluorescence emission which is detected in the far field from a fluorophore located in a thin film between two dielectric interfaces. With the use of the method of Langmuir-Blodgett deposition, thin films of three different thicknesses were deposited on the flat surface of a hemicyclindrical quartz prism. Each film was constructed so as to contain a plane of fluorophores located at a specific distance from the prism/film interface. According to the principle of reciprocity, a distinct angular pattern of fluorescence is predicted for each film type. The close correspondence of fluorescence data curves with theoretical curves lends empirical support to the validity of the principle. The prediction made by this principle of reciprocity is relevant to the analysis of observation angle data obtained from variable angle total internal reflection fluorescence spectroscopy (VA-TIRF) and related techniques.