Longitudinal component of the Poynting vector of a tightly focused optical vortex with circular polarization

We numerically investigated the focusing of optical vortices with the wavelength $\lambda = 532 nm$ and right-hand circular polarization by using a diffractive lens with the numerical aperture NA = 0.95. The simulation was carried out using the Richards-Wolf formulae and the FDTD-method. The focusing of optical vortices with topological charges equal to $\pm 1$ and $\pm 2$ was investigated. It was shown that the focusing of optical vortices with circular polarization by a wide-aperture diffractive lens can produce an intensity distribution with the negative value of the longitudinal component of the Poynting vector.