Why does a hologram appear three-dimensional?
To create holograms, a beam of laser light is split into two beams which travel through an arrangement of lenses and mirrors. One beam bends toward the object. The other travels toward the holographic film. Then the beams meet forming a pattern of light. This has information about the size, shape and depth of the object and gets recorded on the film. Light shining on the developed film is bent and focussed by the pattern to create a three-dimensional image.