Tight focusing of laser light using a polarization converter and an adaptive lens

Tight focusing of laser light using a polarization converter and an adaptive lens is demonstrated. The polarization converter is used to convert the linearly polarized light into a radially polarized light. The adaptive lens is used to focus the radially polarized light on a spot. At the focused spot, a large component of the electric field is along the longitudinal direction, and the focused power density is enhanced. The size of the focused spot can be changed by changing the focal length of the lens. When the focal length of the lens becomes shorter, the focused spot becomes tighter. The mechanisms of the two devices are introduced, and the theory of tight focusing is experimentally supported. Tight focusing of radially polarized laser light with a controllable spot size has potential applications in super-resolution imaging, material processing, and microparticle trapping.