Probing dynamics near surfaces: waveguide enhanced dynamic light scattering

Interfaces and interphases are a vital part of everyday life—since the influence of their proximity might change considerably the behaviour of systems studied. The ability to study motion on the nanometre scale is essential for the understanding of transport phenomena to and from surfaces, thin films or membranes. It is indispensable to have analytical methods with spatio-temporal resolution adapted to these problems and which are non-invasive to obtain untainted results. The small dimensions lead to weak signals and therefore we need experimental setups which are able to amplify them. Here we describe a dynamic light scattering experiment where the evanescent part of waveguide modes is used as the source of light. Using waveguide modes increased the signal-to-noise ratio by a factor of 8 compared to evanescent waves generated by total internal reflection and it allows adjusting the spatial resolution near the interface in situ. This technique monitors changes of the waveguide surface as e.g. adsorption to it.