Effect of radial defect lines in the focalization of unitary polarization order light beams

In this letter, we analyze the effect of the defect line of a theta-cell polarization converter on the focalization of a Gaussian laser beam by means of a high numerical aperture microscope objective. This liquid crystal device is frequently used to convert a linearly polarized laser beam into either a radially or azimuthally polarized beam. The line singularity, that defines the cell axis and characterizes these devices, leads to a pi-shift on the light polarization in moving from one side of the cell to the other, with respect to the cell axis. The shift, although negligible for light filtering and polarization microscopy, can be crucial in applications where a strong longitudinal component of the focused field is needed, such as in aperturless near-field microscopy. In this work, light distribution simulations as well as experimental investigations of the fields at the focal plane are carried out. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3562587]