=================================================================================
Incoherent electrons can either originate from different sources or from two distant points of a large source, meaning no phase relation between the electrons. In electron microscope, due to change of energy electrons after inelastic scattering are incoherent, and plasmons are the primary way of inelastic electron scattering.
Table 4200. Coherency of scattered electrons from a specimen in EM (electron microscope) measurements.
Coherency |
Property |
Coherent |
In phase: preserves the relative phases of the wavelets scattered
from different locations in a material; namely, well-defined
phase relationship between incident and scattered radiation |
Fixed wavelength |
The resolution for coherent imaging is much
worse than that for incoherent imaging |
Useful for diffraction experiments |
Incoherent |
No phase relationship: does not preserve a phase relationship
between the incident wave and the scattered wavelets |
Not useful for diffraction experiments |
The spatial distribution of the scattered
intensity is obtained by summing up the intensities from independent scattering
events |
Incoherent elastic scattering follows the Rutherford scattering law |
The resolution for incoherent imaging is much
greater than that for coherent imaging due to squaring an amplitude distribution |
Incoherent cases: e.g. difference in
wavelength |
More coherent beam |
Sharper diffraction pattern can be obtained |
* When the electrons are treated as waves, their coherency becomes important. |
|