A hologram is a light wave interference pattern recorded on photographic film that can produce a 3 dimensional image when illuminated properly. A hologram is made by a laser beam split into two beams. The reference beam is spread by a lens or curved mirror and aimed directly at the film plate.
The object beam is spread and aimed at the object. The object reflects some of the light on the holographic film plate. The two beams interact forming an interference pattern on the film. This is the hologram. Laser light is needed because it is made of coherent waves. The principle of holography was discovered in Britain by Dennis Gabor in 1948. He was awarded the Nobel price for this discovery in the early 70's.
When the hologram is illuminated from the original direction of the reference beam, a 3 dimensional image of the object appears where the object was originally. Some holograms must be viewed with laser or monochromatic light, and others with white light.
Some of the maim types of holograms areTransmission Holograms: Viewable with laser light. They are made with both beams approaching the film from the same side. Reflection Holograms: Viewable with white light from a suitable source such as spotlight, flashlight, the sun, etc. They are made with the two beams approaching the holographic film from opposite sides. Multiple channel holograms: Two or more images are visible from different angles. There are different types of multiple channel holograms: Simple ones with 2, 3, or a few images each viewed from a different angle. Multiplex: A large number of "flat" pictures of a subject viewed from different angles are combined into a single, 3 dimensional image of the object. A composed hologram. Rainbow holograms: The same image appears in a different color when viewed from different angles.
These are usually reflection holograms made from a transmission original. The image dramatically projects in fromt of the plate toward the viewer. Most holograms in holography museums are of this type. The procedure for making them is quite elaborate and demands precise control of angles.
| what is a laser | how do they work | some of the uses |
| different kinds | who invented lasers | what is a hologram |