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According to the superposition principle, the net displacement is simply given by the vector or the algebraic sum of the individual displacements. Interference is the combination of two or more waves to form a composite wave, based on such principle. The idea of the superposition principle is illustrated in Figure 14.1.1. (a) (b) (c) (d)
1 Huygens’ principle. Diffraction refers to what happens to a wave when it hits an obstacle. The key to understanding diffraction is a very simple observation first due to Huygens in 1678. Say a wave arrives at an opaque screen with a little hole in it.
Diffraction is the concept that is explained using Huygens’s Principle, and is defined as the bending of a wave around the edges of an opening or an obstacle. This principle can be used to define reflection, as shown in the figure.
Huygens’ principle asserts that a wave front can be thought of as many wavelets, which propagate and interfere to form new wave fronts. This is illustrated in Fig. 10.1. The phenomenon of diffraction is then understood as the spilling of wavelets around obstructions in the path of light.
Diffraction by a lattice with a basis: the geometrical structure factor The diffraction conditions (either Bragg or Laue) tells only the location of the diffraction peaks, but not the magnitude. The magnitude of the diffraction peaks are determined by the electron density distribution of the basis.
In order for an interference pattern to develop, the incoming light must satisfy two conditions: The light sources must be coherent. This means that the plane waves from the sources must maintain a constant phase relation. The light must be monochromatic. This means that the light has just one wavelength.
Lecture Video: Diffraction, Resolution. The phenomena related to diffraction are the focus of the lecture. Prof. Lee explains the mathematical description of the diffraction pattern of the wave traveling through a wide slit.
