Scratch Holograms - the only genuine White Light Holograms

Scratch holograms consist of circular grooves in a polished surface, one for each image point, and can be made with dividers on the plastic cover of a compact disk. For observation a more or less point like light source is necessary - it can be white like the sun or may have any color. Described by Wheatstone in the 19th century, scratch holograms were rediscovered in the nineties of the last century and particularly William Beaty developed them to display three dimensional images. Closely related to Poisson’s spot (or Arago’s spot) and caustics, the physics of scratch holograms is based on diffraction and on the conservation of momentum of light during scattering from a scratch or groove. As a consequence scratch holograms are real white light holograms and independent of wave length. We show this theoretically by using Born’s approximation and demonstrate experimentally that scratch holograms can be fabricated by white light interference, where light behaves like a stream of small particles coming from the nozzle of a sand blast unit exiting a tilted slit.