First Laue Equation (AB-CD)=a(cosa,-cosdo)=n, constructive interference: phase difference of two waves n("in-phase") If two in-phase incident waves are deflected by an array of atoms,the deflected waves will not be B in-phase unless their path difference is nA. If the distance between Correlate lattice spacing with X-ray's wavelength. atoms is“a”,then the Laue Fortunately,they are about the same. equation must be satisfiedFirst Laue Equation constructive interference: phase difference of two waves = nλ (“in-phase”) If two in-phase incident waves are deflected by an array of atoms, the deflected waves will not be in-phase unless their path difference is nλ. If the distance between atoms is “a”, then the Laue equation must be satisfied Correlate lattice spacing with X-ray’s wavelength. Fortunately, they are about the same