Abstract
This paper describes a simple procedure to determine the local thickness of a thin anisotropic layer. It also discriminates between isotropic and anisotropic regions, provided a smoothness hypothesis on the refractive index distribution is satisfied. The procedure is based on the analysis of surface plasmon resonance (SPR) data acquired in an imaging mode. The general arrangement of the setup is the Kretschmann configuration. We show, on an azobenzene modified polymer layer, good agreement between atomic force microscopy and optical measurements of thickness variation.
Highlights
Anisotropic thin films are ubiquitous in many fields, from optical technologies to biophysical and cellular studies
Common optical biosensing methods, such as surface plasmon resonance (SPR), optical waveguide spectroscopy (OWLS) and plasmon waveguide resonance (PWR) rely on the existence of discrete, localized modes which can be excited under particular conditions of the incident light
Tiny changes in the boundary conditions of the regions supporting localized modes dramatically change the excitation conditions. This high sensitivity is at the origin of the usefulness of SPR, OWLS and PWR
Summary
Anisotropic thin films are ubiquitous in many fields, from optical technologies to biophysical and cellular studies. Tiny changes in the boundary conditions of the regions supporting localized modes dramatically change the excitation conditions This high sensitivity is at the origin of the usefulness of SPR, OWLS and PWR. [15] describes a setup very similar to ours, without any analysis of anisotropy determination This short review shows that the optical characterization of anisotropic films requires either complex setups or additional information (such as in the two-color method) which are not always available. We introduce an image analysis tool that discriminates between isotropic and anisotropic media We compare both topography and optical indices to, respectively, AFM measurements and published results in the literature, obtaining respectively good and qualitative agreement. Our imaging setup will be called Plasmon Waveguide Resonance Imager (PWRi)
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