In this paper we will discuss a few basic concepts concerning the use of evanescent optical fields for the excitation of fluorescent chromophores placed near the interface. The observation of enhanced fluorescence from chromophores excited by surface plasmon and waveguide modes will be presented and discussed. We attribute the enhancement to the near-field interaction between the chromophores and the increased photonic mode density by surface plasmon and waveguide modes. We determined limits of detection (LOD) of DNA hybridisation using the same sensor architecture by surface plasmon fluorescence spectroscopy (SPFS) and optical waveguide fluorescence spectroscopy (OWFS). Both SPFS and OWFS techniques have the same detection principle using an enhanced electromagnetic field to excite fluorophores and make it possible to monitor DNA hybridisation in real-time with high sensitivity. The relative photonic mode density of each mode was calculated under the resonance condition, and these values are reflected in the LOD values.
Scattering optical waveguide microscopy is a novel imaging technique, that allows for the microscopic characterization of thin film samples by using the evanescent field of a guided optical wave as the illuminating light source. The image contrast is generated by the scattered intensity of the thin film sample within the evanescent field. Excellent lateral resolution (< 1 micrometers ) is demonstrated for an evaporated SiOx grating. Immersion microscopy has been performed with an additional cuvette in the same setup. The contrast of the image is investigated with respect to mode number and polarization of the illuminating, propagating waveguide mode and the surface roughness of the sample.
The coupling of p-polarized waveguide modes into waveguide- surface plasmon coupled modes is a promising concept to combine the features of propagating waveguide modes with the resonant field enhancement of surface plasmons. We demonstrate a waveguide device which allows to couple more than one TM mode to the surface plasmon. For a given waveguide device and a fixed laser wavelength the development of the imaginary part, K, of the propagation constant, Neff, of the waveguide-surface plasmon coupled modes are simulated and the results are compared with experimental results. The waveguide losses are in perfect agreement with the simulations. Due to the resonant nature of the waveguide-surface plasmon coupled modes, which was found by the simulations, the waveguide attenuation is very sensitive to the refractive index of the subphase outside of the waveguide structure. This resonant behavior could be confirmed experimentally.
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