> > 1. In every description of Braggs' law I've seen, the in-coming waves > > have to be in phase. Why is that? Given that the sources used for > > diffraction studies are mostly non-coherent. > > Think of Bragg's Law as explaining what happens to a single photon > that is probabilistically scattered by every atom in the lattice. > It's perfectly coherent with itself. Why does the photon not diffract at all angles then, since one 'part' of the photon will never have a different phase from another 'part'? If you are correct that it is a single photon diffracting, it would suggest that at some point the photon is in-coherent with itself thus the need to have a diffraction condition for specific angles.
It would make more sense to me in such a case, if we interpreted Braggs' law as the condition under which the photon keeps it's 'internal coherence but instead we talk of constructive and destructive interference! > This idea should be no stranger than textbook illustrations of the > result of sending a single particle through a narrow slit or pinhole. > The interference effects follow the expected predictions even for > illumination by one particle at a time. The mathematics works but doesn't necessarily mean the current interpretation of the mathematics has any resemblance to what actually happens in reality.
