NSOM Technique
While traditional optical spectroscopy has diffraction limited
resolution of no better than 1/2 the wavelength (~200 nm for visible light),
near-field spectroscopy surpasses this resolution limit and achieves subwavelength
resolution (20 nm - 200 nm). In near-field spectroscopy, light propagates
through a subwavelength size aperture (20 nm - 200 nm) in an opaque screen.
Within the near-field the light is confined to an area on the order of
the size of the aperture. The resolution of NSOM depends on the size
of aperture used and the distance to the sample, but not on the wavelength
of light. An image is generated by irradiating a small portion of
an object placed within the near-field of the aperture (tip) and raster
scanning the sample.
Figure 1. A sample is irradiated by placing it within a few
nanometers of the aperture.
NSOM Schematic