Tight focusing of laser light propagated through subwavelength micropolarizer using Fresnel zone plate

We discuss a four-Sector transmission Polarization Converter that enables the conversion of linearly polarized incident light into an azimuthally polarized beam. The resulting azimuthally polarized beam is characterized by a phase shift of pi between the diametrically opposite beam points. Using scanning near-field optical microscope we experimentally show that by placing a Fresnel zone plate of focus 532 nm behind the four-sector micropolarizer, light can be focused into a subwavelength focal spot with smaller and larger sizes measuring FWHM = 0.46 lambda and FWHM = 0.57 lambda. Numerically obtained focal spot of the transverse E-field component, which is measured by our scanning near-field optical microscope, has diameters FWHMx = 0.42 lambda and FWHMy = 0.59 lambda.