A hologram is often described as a three-dimensional picture. While this is a good way to get a general idea of what you would experience looking at one, holography has very little in common with traditional photography.

While a photograph has an actual physical image, a hologram contains information about the size, shape, brightness and contrast of the object being recorded. This information is stored in a very microscopic and complex pattern of interference. The interference pattern is made possible by the properties of light generated by a LASER.

The light reflected by a three dimensional object forms a very complicated pattern that is also three-dimensional. In order to record the whole pattern, the light used must be highly directional and must be of one color. Such light is called coherent. Because the light from a laser is one color, and leaves the laser with one wave in perfect step with all others, it is perfect for making holograms.

When you shine a light on the hologram, the information that is stored as an interference pattern takes the incoming light and re-creates the original optical wavefront that was reflected off the object. Your eyes and brain now perceives the object as being in front of you once again.