3.3. Diffraction
203
2. An electron with kinetic energy 100 keV is normally incident on
a circular object of radius 100 nm. Estimate the shortest distance
Z for which the Fraunhofer approximation is a valid estimate of
the downstream amplitude.
3.3.3 Amplitude in the Gaussian image plane
We assume an object plane at axial coordinate z O , a thin lens
of focal length f at z L , and a Gaussian image plane at z I . This
geometry is shown in Figure 3.11. The relationship between the
Figure 3.11: Image formation for a point object at r O .
203
2. An electron with kinetic energy 100 keV is normally incident on
a circular object of radius 100 nm. Estimate the shortest distance
Z for which the Fraunhofer approximation is a valid estimate of
the downstream amplitude.
3.3.3 Amplitude in the Gaussian image plane
We assume an object plane at axial coordinate z O , a thin lens
of focal length f at z L , and a Gaussian image plane at z I . This
geometry is shown in Figure 3.11. The relationship between the
Figure 3.11: Image formation for a point object at r O .