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.

 

fig 1: near-field aperature
 
Figure 1.  A sample is irradiated by placing it within a few nanometers of the aperture.

NSOM Schematic