Phase-sensitive imaging of diffracted light by single nanoslits: measurements from near to far field.

We perform phase-sensitive imaging of optical wavefront emanating from a single nanoslit and propagating into free space by using scattering type near-field scanning optical microscope combined with an optical interferometer. By analyzing polarization resolved optical amplitudes and phases, the propagation directions of surface waves are determined and the phase difference between two orthogonal polarization components of the surface wave are discussed for increasing distance from the slit.