Figure 2: Near-field measurements on a single hole and two holes.

(a,e,i) The absolute value of measured complex NSOM signal L_y. (b,f,j) The real part of L_y. (c,g,k) The absolute value of the 2D Fourier transform of L_y, the k-vector distributions obtained. (d,h,l) Are polar plots of the SPP intensity on a logarithmic scale. These are obtained from the k-space distribution of both L_x and L_y. The field distribution of a single hole is on the top row. For the two hole system the phase of the holes is in-phase (e–h) or half a cycle out-of-phase (i–l). Because our system is symmetric, the k-space image is only shown for positive values of k_y. The scale bars represent a length of 2 μm and the incident polarization was along the y-direction (indicated with the arrows in (i,j). In the polar plots the experimental data is plotted in green while the black lines show the modeled radiation patterns of the SPPs according to Equation 1. The hole spacing is 950 nm.