We investigate the ability of the bow-tie slot antenna to generate intense optical spots below the diffraction limit. A commercially available finite-difference time-domain electromagnetic modelling software is used in the numerical simulations. The finite-difference time-domain software is first compared to analytical results at optical frequencies to verify its accuracy. We then present numerical simulations for various geometries involving apertures on thin films and the bow-tie antenna. The transmission efficiency and optical spot size of the bow-tie antenna are compared with those of rectangular and circular apertures on thin metal films. We also investigate the effects of material composition, frequency, and antenna geometry on the near-field radiation pattern using numerical simulations.