Fig. 2.

(a) Back focal plane image of objective lens for linear polarized incident wave calculated with NA of 1.65, with immersion medium with refractive index of 1.78 and incident wavelength of 633 nm, where light was illuminating a 47 nm thick uniform gold in water ambient. (b) Schematic diagram showing how surface plasmons propagation on the surface of the uniform gold substrate, note that the bright areas correspond to strong SP excitation (c) A portion of the wavefront of unfocused SP beam propagating from left to right which is slightly shifted by the analyte, giving a small average phase shift (d) shows the array structure simulated with RCWA. The position ‘M’ represents the mid-point position remote from the analyte where the size of the unit cell is adjusted to give a response similar to bare gold.