Generation of sub wavelength super long dark channel using azimuthally polarized annular multi-Gaussian beam

We investigate the interesting focal properties of phase modulation azimuthally polarized annular multi Gaussian beam employing a high numerical aperture (NA) lens on the basis of vector diffraction theory. We observe that our proposed system generates a sub wavelength focal hole of (0.43 uplambda ) having large uniform focal depth of (84 uplambda ) . This kind of nondiffracting focal hole is called dark channel, which may have applications in atom optical experiments, such as with atomic lenses, atom traps, and atom switches.