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Holography is the creation of three-dimensional images called holograms. The process is similar to that of photography except that rather than recording an image, it captures light fields. In order to start the process, two beams of light are created by the refraction of one light beam directed at a mirror. One beam is directed at the object to be documented, while the other illuminates the recording medium. The interference between these two beams creates a ghostly 3D image when it is illuminated with a laser beam.
Each of the beams used in the process of holography have a name. The ray that lights up the item to be captured is called the object beam. It is offset by the reference beam which shines on the recording medium. Once the hologram has been developed, it is displayed by shining a laser beam through the image. It is placed in the opposite direction and at an angle identical to the reference beam.
Holography images are recorded on photographic plates. Though the process of collecting images is somewhat similar to regular photography, more visual information about the specific object is being collected than with a photograph. The scattered effect of the reflected light beams captures depth and detail that a camera lens cannot record. A camera captures an image using light that does not penetrate the angles of the object, but rather illuminates the entire area, either naturally or via artificial lighting.
As the light beams used in holography only focus on certain objects, the surroundings are not included in the captured image. The photographic plate records the visual interference that results from the light hitting the object. It does not capture the object as it appears to the naked eye.
In order for holography to work correctly, the light beams must be stable throughout the image capture process, a state known as coherence. For this reason, lasers tend to be the most frequently used source because they are easier to keep completely still. Other sources of light can be used, however. It is possible to use any two light sources to create a hologram as long as they can maintain a sufficient coherence length.
For a hologram to be properly displayed, light must be shined through the captured image precisely where the reference beam was originally directed. Otherwise, the image will be distorted. Once the beam is in place, the plate with the captured image can be moved to show other sides of the object as if it is still present.
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