Figure 4.4.2.3 

Momentum-space representation of Bragg scattering from a crystal moving (a) perpendicular and (b) parallel to the diffracting planes with a velocity v_k. The vectors k_L and refer to the incident and reflected wavevectors in the laboratory frame of reference. In (a), depending on the direction of v_k, the reflected wavevector is larger or smaller than the incident wavevector, k_L. In (b), a larger incident reciprocal-space volume, Δv_L, is selected by the moving crystal than would have been selected by the crystal at rest. The reflected reciprocal-space element, , has a large divergence, but can be arranged to be normal to , hence improving the resolution .