Double Diffraction White Light Imaging: First Results with Bidimensional   Diffraction
  The double diffraction of white light can produce a thin-prism-like image in certain conditions by using ordinary diffraction gratings. The diffractive deviation of rays happens mainly in one direction because the diffracting elements are straight and parallel. We show similar images using elements where diffraction happens in both directions: spiral grooves discs. Some differences between the straight-groove and the almost circular curved-groove cases are described. 
Jose J Lunazzi, Noemi I Rodriguez Rivera