Difference between Bragg and Laue Diffraction?

[etmsni]

Hi! I am confused about the difference between the Bragg and Laue Diffraction. It seems that both arrive at the same result, but the assumptions for both are different?

 

[Gokul43201]

What are the differences in assumptions? I can't think of any. They both deal with elastic scattering off a periodic lattice.

 

[etmsni]

The Bragg condition considers lattice objects that are grouped in families of planes, and the incident radiation is specularly reflected. The Laue condition doesn't require the assumption of particular planes and spacings, and doesn't require that reflection be specular.

 

[Gokul43201]

The Laue criterion is dependent upon the construction of a reciprocal lattice. That requires the existence of the direct lattice (consisting of families of planes defined by Miller Indices), upon which the Bragg condition is derived.

The apparent difference regarding specular reflection is an artifact of the way in which Bragg reflection is commonly depicted - by looking at only one family of planes. In reality, through every point in the real lattice, one can construct a virtually infinite number of lattice planes, each of which produces a specular reflection in a different direction.