a surface relief hologram built up from an array of tiny diffractive gratings arranged at certain angles. The ‘dots’ are a point at which two microscopic beams of laser light meet at an angle and produce an interference pattern. In a dot matrix machine, a mechanical arrangement moves this point of light in a matrix pattern relative to a photosensitive plate. According to the final image required, the angle at which each dot is exposed into the matrix is determined by mathematical calculation. It is thus possible to construct fully synthetic images of objects that never existed in real life.