When Bragg's law is explained, the word "diffraction" is used. But, as far as I see the picture above which is often added to the explanation, it seems what happens is not diffraction but just reflection.
I believe diffraction and reflection is different. Why is the word "diffracion" used?
Thank you in advance.
In Fraunhofer diffraction, every points at the aperture (the opening) are regarded as secondary sources. Mathematically, the wave fronts are undergone Fourier transform of a step function over the aperture.
We extend the idea to a crystal lattice. Waves "diffracted" from each particles (atoms, ions, molecules and so on) are regarded as point sources (at least to a good approximation). More precisely, the particles scatter the incoming waves with regular phase differences. The diffracted waves are hence the Fourier transforms of periodic delta functions (layer by layer with constant phase shift).
