As structures become very small (which for microscopy, means smaller than the optical diffraction limit) their interaction with light changes.  The result is that using standard far field optical configurations will no longer allow spatial information about the structure (for example, size and shape) to be obtained.

The diagram below illustrates the interaction of a progressive plane wave with structures which have dimensions greater than, and less than, the wavelength of the light.  With large structures (dimension > wavelength) the plane wave is deformed within the far field.  However, with very small structures (dimension < wavelength) a near field evanescent wave is established which contains the nanometer structural information.  However, as the evanescent wave moves into the far field it is deformed and soon loses the near field structural information.

To access this nanoscale information it is necessary to work with near field optics, such as NSOM/SNOM or Raman-AFM tip enhanced Raman scattering (TERS).


Raman systems from HORIBA Scientific are designed for performance and flexibility, and as such can be combined with AFM units from most manufacturers.  Such combined Raman-AFM systems allow the benefits of both Raman and AFM to be explored on a single bench top unit, and offer the capability to explore tip enhanced Raman spectroscopy (TERS) for true nanoscale Raman analysis.

Technical Notes

RA-TN01 - Introduction to Raman Imaging