Broadband wide-angle dispersion measurements: instrumental setup, alignment, and pitfalls.

The construction, alignment, and performance of a setup for broadband wide-angle dispersion measurements, with emphasis on surface plasmon resonance (SPR) measurements, are presented in comprehensive detail. In contrast with most SPR instruments working with a monochromatic source, this setup takes advantage of a broadband∕white light source and has full capability for automated angle vs. wavelength dispersion measurements for any arbitrary nanostructure array. A cylindrical prism is used rather than a triangular one in order to mitigate refraction induced effects and allow for such measurements. Although seemingly simple, this instrument requires use of many non-trivial methods in order to achieve proper alignment over all angles of incidence. Here we describe the alignment procedure for such a setup, the pitfalls introduced from the finite beam width incident onto the cylindrical prism, and deviations in the reflected∕transmitted beam resulting from the finite thickness of the sample substrate. We address every one of these issues and provide experimental evidences on the success of this instrument and the alignment procedure used.