Tightly focused light field with controllable pure transverse polarization state at the focus

We report on a facile and flexible scheme for producing the controllable pure transverse polarization state at the focus within a tightly focused field. Toward this aim, a special type of hybrid vector beam exhibiting unusual "8-type" mapping tracks of azimuthal polarization states on the Poincaré sphere is employed. Due to the peculiar polarization structures, at the focus, there is only the transverse component, while the longitudinal component is zero for any 8-type vector beam. More strikingly, the transverse polarization state at the focus is exactly the same as that of the cross point of the 8-type mapping track. Benefiting from this appealing polarization relationship, an arbitrary transverse polarization state can be easily achieved at the focus via altering the mapping track of incident vector beams. These results may have potential applications in nano and spin photonics.