On 12 January 2012 10:33, Dirk Kostrewa <kostr...@genzentrum.lmu.de> wrote: > My understanding of coherence is a constant phase relation between waves.
Correct. For a perfect crystal all the unit cells are identical so they scatter in phase and this gives rise to the interference effect we see as Bragg spots, as you say arising from a constant phase relation in specific directions. For a disordered crystal the unit cells are not the same: this destroys the interference effect but there's still a constant phase relation in any specified direction so it's still coherent. > Of course, this breaks down for inelastic scattering, but (in)coherence can > also be described without any change in wavelength. That's not the definition of incoherence used by the physicists. Of course you're free to redefine it but I think that just confuses everyone. Cheers -- IAn
