> You are just using the coherent fraction of the beam. My point is that Braggs' law as currently understood does not preclude the diffraction from waves which were non-coherent before hitting the sample
> It is not clear at all how you arrive to that condition. By definition, if > two waves are non coherent, you cannot define a "phase difference". The > phase difference is continuosly changing at random with non coherent waves. if the phase difference between two waves is y, the extra distance the second wave has to travel to again be in phase is y*lambda/2pi if this distance is the same as the 2dsin(theta), the diffraction condition will also be met. My understanding is that coherence has to do with the phase not the wavelength. Only when the wavelengths are also different will the phase difference be changing continuously. No? > ???? You do not annihilate energy with interferences, you just spread it > differently. Apart for conservation of energy, Thermodynamics is seldom > involved in these considerations. My point is that destructive interference implies that energy is destroyed which does not make sense. If as you say the energy is simply spread differently, what would be the mechanism/geometry of this spreading? > A complete lack of coherence leads simply to adding intensities of the two > waves. On the contrary. complete lack of coherence leads to destructive interference. No? Perfect coherence leads to the amplitudes adding up.
