Glossary of Terms

beamsplitter
A device used to divide the light from a laser into two separate beams--the reference beam and the object beam. It consists of a partially transparent mirror that reflects part of the laser beam and transmits the rest.

coherent light
Light which is of the same frequency and is vibrating in phase. A laser produces coherent light.

film
Whether photographic or holographic, film consists of light sensitive chemicals (the emulsion) spread on a surface. A film's resolution measures the ability to distinguish between details. Because holographic films must be able to record very detailed information, they have a resolving power of 50 or more times that of photographic film. They require either exposure to a high-intensity pulsed laser or a long exposure to a continuous wave laser. Holographic film is developed in a manner similar to photographic film, by bathing it in a series of chemical agents.

hologram
Unlike photography which records an image as seen from a single viewpoint, a hologram is a record of an image as seen from many viewpoints.

holography
A medium for bending and focusing light that uses the interference of monochromatic object and reference waves to record and reproduce multiple two-dimensional images for three-dimensional viewing.

interference pattern
When two waves overlap, their amplitudes add at every point. This results in an interference pattern which records the relative phase relationship between the two waves, storing each individual wave's characteristics. This is how a hologram works.

laser
A laser is a device that produces a concentrated beam of coherent light. Some, called continuous wave lasers, produce a continuous beam of light. Others, called pulsed lasers, emit more light in brief pulses that are able to freeze motion.

lenses
Lenses are devices that redirect light. In photography, lenses are used to focus an image for the film. Holographers use lenses to widen a laser's beam to illuminate all of the object being holographed.

object beam
The light from a laser beam that illuminated the object and is reflected to the holographic film.

phase
The position of a wave in space, measured at a particular point in time.

reference beam
The portion of a laser beam that goes directly to the holographic film. The interference pattern that results from the object beam meeting the reference beam at the holographic film is recorded on the film.

reflection hologram
One that forms an image by reflected light. Reflection holograms are lit from the front, reflecting the light to the viewer.

transmission hologram
One that forms an image from the light passing through the holographic emulsion. Transmission holograms are lit from behind, bending the light as it passes through the hologram to your eyes.

white light
Light that contains most of the wavelengths in the visible spectrum, such as light from the sun or from a spotlight. White light is incoherent, while laser light is coherent. A white light transmission hologram, or rainbow hologram, is one which can be displayed using ordinary white light. Early holograms required viewing with coherent laser light.

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