Fig. 1. Sketch showing the systems of coordinates used throughout the text.

Fig. 2. Left and middle columns: pattern of the (top – plots A and B) and (bottom – plots D and E) vector fields at  and for an , OAP. Right column: intensity (top – plot C) and field pattern (bottom – plot F) at . The beam incident on the OAP is supposed to be polarized along (or , corresponding to ).

Fig. 3. Pattern of the vector field at the times (top) and (bottom), for an , OAP.

Fig. 4. (top) and (bottom) field patterns at  for an , OAP, with an incident beam polarized along (or , corresponding to ).

Fig. 5. (top) and (bottom) field patterns at  for an , OAP, with an incident beam polarized at with respect to (or , corresponding to ).

Fig. 6. Map of the ratio (calculated at ) of the field longitudinal component to the transverse component , for an , OAP and a beam polarized along .

Fig. 7. Maps of the ratio of at  to the corresponding value at , calculated for a beam polarized along () and focused with the following OAPs: , (plot A), , (plot B), , (plot C), , (plot D).

Fig. 8. Plots of the parameter (defined in the text) vs. the off-axis angle (top) and the (bottom). In the first plot, data for both the () and () polarizations are shown, while only the data for the polarizations are shown in the second plot. The results of fits with functions of the form given in equation (17) are also shown for the case .