Using a new technique called Near-field Scanning Optical Microscopy (NSOM), scientists are able to spatially resolve optical signals that originate from points that are closer together than a wavelength of the light. The key element in NSOM is a fiber optic cable that has been sharpened such that it ends in a sub-wavelength diameter tip. This tip is coated with aluminum such that it leaves only a sub-wavelength aperture uncoated at the very tip. Light is seen emanating from the tip in the image shown below. This image was taken under a conventional optical microscope.

Optical signals are transmitted through the sub-wavelength aperture while the tip is simultaneously scanned over a surface using a scanning probe technique similar to non-contact AFM. The response of the sample to the light emanating from the tip is recorded as a function of the tip position over the sample. In this manner the sample is imaged with very high resolution in the NSOM experiment.

The high spatial resolution makes NSOM a very general advancement in optical microscopy. As such, NSOM can, in theory, be combined with any spectroscopic technique to gather spectra from small regions of a sample. IR, Raman, visible, and UV, as well as NSOM fluorescence, photoluminescence, photoconductance, and magnetooptical (MOKE) spectroscopies have been investigated. In each case, combining the wavelength regime or spectroscopic technique with NSOM made it possible to gather unique and highly spatially resolved data concerning the composition and physics of surfaces on short length scales (tens of nanometers).