(a)-(d) and (e)-(h) are experimental NSOM images and simulations of the near-field distribution above the Plasmonic Vortex Lens at right-handed and left-handed circular polarization (respectively).

(c) Ez distribution of the near-field calculated by the RCWA. The number of node lines is five, which indicates that the topological charge of the SP vortex is l ) 5. The white arrows in (a)-(c) denote the directions of the rotation of the polarization. (d) Comparison of the intensity profiles. The red dashed line corresponds to the result of the theoretical model, i.e., the square of the absolute value of the fifth order Bessel function of the first kind. The blue solid line depicts the field intensity along the dashed line in the NSOM image. The black dotted line shows the field intensity along the dotted line in the RCWA image (Figure 3b). (e), (f), (g), and (h) correspond to (a), (b), (c), and (d), respectively, but from the left-handed circularpolarization beam.

Byoungho Lee et al Nano Lett. 2010, 10, 529-536  

Experimental setup for NSOM imaging of light distribution above Plasmonic Votrex Lens using Nanonics MultiView 4000TM system which has a free optical axis from top and bottom for bottom illumination of the sample and upright view (up to 100x) for tip-sample accurate positioning.

Byoungho Lee et al Nano Lett. 2010, 10, 529-536