Experimental verification of focus tailoring using circularly polarized vortex beams with annular pupil mask

The focusing properties of circularly polarized vortex beam are experimentally verified by examining two-photon fluorescent emission patterns inside an fluorescent microsphere. Very good agreements between the experimental and theoretical results have been obtained. Annular pupil masks are used to tailor the profile at the focus. When an circularly polarized beam with the appropriate handedness is used in combination with an annular pupil aperture, a strong longitudinal component is observed, which results in a raised center and a smaller focal spot. This interesting focusing property can be utilized in applications that require a distinct longitudinal component.