Bragg diffraction pattern of the organic dye molecule phthalocyanine at an incidence angle θgrat=5(5) μrad. Panel (a) shows the false color diffraction image. Panel (b) shows the averages of 20 μm high stripes, smoothed with median and Savitzky–Golay  filters, and annotated with their corresponding velocities in m/s. The velocities are determined by comparison with a diffraction pattern produced by a material grating . The laser grating waist for this measurement is wy=57(3) μm and the collimation slit width is 11.5 μm.