Fringes, diffraction

Experimentally, this technique is very similar to the TDI technique described above. A laser beam is incident normally on a diffraction grating or a preferentially scratched mirror deposited on the surface to obtain the normally reflected beam and the diffracted beams as described above. Instead of recombining the two beams that are located symmetrically from the normally reflected beam, each individual beam at an angle d is monitored by a VISAR. Fringes Fg produced in the interferometers are proportional to a linear combination of both the longitudinal U(t) and shear components F(t) of the free surface velocity (Chhabildas et al., 1979), and are given by... 

In order to observe fringes, the screen should be placed in the regime of Fraunhofer diffraction where F/B B/X. In practice, such an interferometer can be realized by placing the stop immediately in front of a collecting optics, e. g., a lens or a telescope, and by observing the fringes in its focal plane (F = fes). 

Usually, at least several hundreds of fringes are measured and characterized. Taking the classical example of X-ray diffraction, coherent domains are defined by the stacks of polyaromatic layers (Figure 2). The coherent domains are distinguished from the single layers and their relative... 

Figure 4. Electron diffraction pattern (bottom left) of a typical disordered wol-lastonite specimen. Evidence of the disorder comes from the streaked (Tc odd) diffraction spots. The fringes shown in the dark-field image (a) are 7 A apart. Dark-field image b, taken from the streaked diffraction spots, shows a one-dimensional image of the disordered wollastonite. Dark-field image c shows a two-dimensional image which shows the haphazard stacking of the triclinic and monoclinic...

Fig. 4.4.3 High-resolution electron micrograph and electron diffraction pattern. (A) Sample II the mean diameter and lattice fringe of particles X and Y were 7.7 nin, 0.374 nm. and 7.1 nm, 0.397 nm, respectively. (B) Sample V the 15.4-nm particle was viewed along the [0011 zone axes with the 100 lattice spacing of 0.397 nm. (From Ref. 10.)...

There is a direct analogy with the fringe pattern that is seen in a Young s double slit experiment, in which the diffraction pattern from two slits produces periodic fringes whose spacing varies inversely with the separation of the slits. The oscillations can also be interpreted in terms of the distortions of the reflected wavefronts in Fig. 7.2 at the Rayleigh angle (Atalar 1979). 

Figure3.15 (A) Small-angle electron diffraction pattern recorded from an individual Au NCS (B) HRTEM micrograph showing the supperlattice fringes in the hep system. (C) Stacking model of Au NPs in the hep system. Reprinted with permission from reference [168]. Copyright 2003 American Chemical Society.

---