Purpose:Analog to diffraction of electrons or x-rays by a powdered crystal.
Description:The laser creates a diffraction pattern of a wire mesh, a series of dots forming a square array. If the mesh is rotated a few times per second circles are formed, representing the random orientation of a powdered crystal target. Circles with the lowest combined order number are brighter. Note that in the picture, due to the short exposure time only segments of each circle are seen. Because your eye has a longer exposure time complete circles are seen.