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Scattering and diffraction

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This is a very good question. Often, these two concepts are confused. Here, I will only offer some personal, superficial understandings regarding electromagnetic waves This is a very good question. Often, these two concepts are confused. Here, I will only offer some personal, superficial understandings

Scattering and Diffraction share some commonalities. At least, when describing their concepts or imagining their physical images, both physical processes involve changing the original propagation direction of electromagnetic waves 。

They have many commonalities, but also many differences. Generally, it is considered that scattering is an incoherent process while diffraction is a coherent process . This seems quite clear. When discussing diffraction, we always cannot avoid interference, but when discussing scattering, we rarely discuss interference. This is evident from their mathematical expressions; the description of the diffraction process starts from the perspective of waves, while the description of scattering often considers particle or wave properties.

Besides the above perspectives from waves or particles, or from coherent or incoherent processes, I once saw a sentence, but I have forgotten the source. The general meaning is: " Diffraction is the macroscopic manifestation of microscopic scattering." ”

I think this sentence makes a lot of sense. Scattering is generally considered to be the change in the propagation direction of electromagnetic waves at the discontinuity of the refractive index of the material . Generally, different types of scattering are classified according to the size of the discontinuous medium. In short, according to the previous sentence, it can be considered that when propagating electromagnetic waves encounter a region with non-uniform refractive index, for example, when encountering particles , causing the electromagnetic waves to propagate in all directions , this is the basic meaning of scattering. If these scatterings form a specific constructive interference, for example, when electromagnetic waves encounter periodically arranged particles , these scattering behaviors interfere constructively, forming diffraction in a specific direction . This better explains "Diffraction is the macroscopic manifestation of microscopic scattering." The illustrations in the literature of near-field and far-field scattering and diffraction are consistent with the above ideas.