“…1, which is similar to the one we used for making SHG holograms of real one-, two-, and three-dimensional ͑3D͒ objects. Before illuminating the mask, the o-beam was passed through a diffuser ͑S͒ to randomize its wave front 13,14 and to scatter it over an angle of 50 mrad. Quanta-Ray GCR-4, Spectra-Physics Inc., Mountain View, CA͒ was split into two beams, one 10% of the other in energy.…”