R. Hillenbrand and F. Keilmann
Physical Review Letters 80, 3029 (2000)
Optical phase contrast has for the first time been observed on a nanometer scale, with a near-field microscope of scattering type that maps the complete optical field of amplitude and phase. Backed by quasielectrostatic theory, we demonstrate the significance and experimental accessibility of even complex optical constants on a subwavelength scale. Further, our method can separate the near-field response from background artifacts and thus is expected to enable nanoscale optical mapping of even topography-rich objects such as resonant clusters and macromolecules.