Schematic representation of the ATR configuration used to excite the 1D grating. In the theoretical model, the space is divided into three regions: the Ge prism (region I), the grating (region III), and the space in between (region II). -polarized incident light undergoes a total reflection at the interface creating evanescent fields in region II.
Specular reflectivity showing minima associated with the first-order cavity mode excited at with a propagating light and presenting a FWHM of (full line) and at with a FWHM reduced by a factor of 6 in ATR configuration (dotted line) for an incident angle in both cases. The vertical arrow indicates the position of the surface-plasmon excitation obtained in ATR.
Experimental (full line) and calculated (dotted line) reflectivity spectra measured as a function of the incidence angle, all other parameters being fixed. The lower wave number structure corresponds to the first-order cavity mode whereas that at higher wave number signs the surface-plasmon resonance. The best agreement between the theory and the experiments is found for a distance and incidence angle (a), 23.5° (b), 26.5° (c), 29.5° (d), 32.5° (e), and 35.5° (f).
Dispersion relation of the excited modes defined from the minima position in the specular reflectivity. The energy of each mode is represented as a function of the parallel momentum in units of and given by . The white background region corresponds to the dispersion of the modes excited by propagating light. ATR configuration allows to investigate part of the region under the light cone, represented by the light gray. The white squares indicate the experimental points, whereas the black and white dots are calculated. The CM and SP symbols stands for the cavity modes and surface-plasmon excitations.
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