Near-field amplitude and phase recovery using phase-shifting interferometry

Scattering-type scanning near-field optical microscopy has allowed for investigation of light-matter interaction of a large variety of samples with excellent spatial resolution. Light incident on a metallic probe experiences an amplitude and phase change on scattering, which is dependent on optical sample properties. We implement phase-shifting interferometry to extract amplitude and phase information from an interferometric near-field scattering system, and compare recorded optical images with theoretical predictions. The results demonstrate our ability to measure, with nanoscale resolution, amplitude and phase distributions of optical fields on sample surfaces. The here-introduced phase-shifting method is considerably simpler than heterodyne methods and less sensitive to errors than the two-step homodyne method.