Surface Plasmon Resonnance (SPR) techniques have been mostly set-up as angular reflectivity
interrogation mode using quasi-monochromatic light or as spectral reflectivity interrogation mode at one given
wavelength, providing information about variation of effective optical thickness ▵n.e above the metal surface. In this
communication we present a dual mode sensor working both in angular and spectral interrogation modes. A white light
illuminates the sensor surface and the reflectivity spectra in TE and TM polarization are measured with a spectrometer.
By changing the angular coupling conditions, a complete reflectivity surface R(θ, λ) can be measured. The 2D
reflectivity decrease valley is affected by both the real and imaginary part of the optical index of the dielectric medium as
well as their spectral dispersion. With such experimental data set, it is possible to back calculate the dispersion of the
complex refractive index of the dielectric layer. This is demonstrated using a turquoise dye doped solution. According to
the Kramers-Kronig relations, the imaginary part of the refractive index for an absorbing medium is proportional to the
absorption while the real part presents a large dispersion around the absorption wavelength. The reflectivity surface R(θ, λ) was measured from 500 nm to 750 nm over about 8° angular range. The whole complex refractive optical index of the
doped solution, absorbing around 630 nm, was reconstructed from the SPR reflectivity experimental data, using a
homemade program based on an extended Rouard method to fit the experimental angular plasmon data for each
wavelength. These results show that the classical SPR technique can be extended to acquire precise spectral information
about biomolecular interactions occurring on the metallic layer.