  We experimentally demonstrate for the first time that a radially polarized
field can be focussed to a spot size significantly smaller (0.16(1) lambda^2)
than for linear polarization (0.26 lambda^2). The effect of the vector
properties of light is shown by a comparison of the focal intensity
distribution for radially and azimuthally polarized input fields. For strong
focusing a radially polarized field leads to a longitudinal electric field
component at the focus which is sharp and centered at the optical axis. The
relative contribution of this component is enhanced by using an annular
aperture.
