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Holographic Storage: How It Works (Page 2/4)

Posted: June 26, 2000
Written by: Tuan "Solace" Nguyen

Types of Holograms (cont.)

Real Image Holograms (H-2's)

These are usually reflection holograms made from a transmission original (H-1). The image dramatically projects in front 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.

Mass-Produced Holograms

Embossed: Made by stamping on foiled backed Mylar film using a metal master (most common method).

Polymer: Made from light sensitive plastic. The Polaroid Corporation mass produces holograms by this method.

Dichromate: Very vivid holograms on jewelry, watches, etc. They are recorded on a light sensitive coating of gel that contains dichromate.

What can holography technology be used for?

Holographic Art: Holography museums, advertising, postage stamps, jewelry, etc.

Security from Forgery: credit cards, tickets, etc.

Optical Devices: Holographic lenses, diffraction gratings, etc. These are holograms in which the "object" is a mirror or a lens. A flat mirror as an object produces a diffraction grating. A lens or a concave mirror as the object produce a hologram that behaves like a lens. These holographic lenses are lighter than traditional lenses and mirrors and they can be designed to perform more specialized functions such as making the panel instruments of a car visible in the windshield for enhanced safety.

Holographic Interferometry: A very precise technique for measuring changes in the dimensions of an object. It is useful in industrial stress analysis, quality, control, etc.

Pattern Recognition: Uses electro-optical devices with computers to interpret what is "seen" by a machine. It is useful in military applications of lasers and holographic optical devices.

Medical Applications: Combining CAT scans into a 3-dimensional image; a multiplex. It’s useful as ultrasound holography, etc.

Other: Holographic computer memory storage, holographic microscopy, holographic radar, etc.

Holographic Storage

Well, we’ve all been waiting for this point -- how do we store information using holographic technology?

Well, like first principles, the storage technology is based on principles of holography; it will use the concept of beam interference patters caused by interacting laser beams.

The following is a diagram of how complex the assembly is to be able to use the technology.

IBM's Almaden Research Center has built a precision Photorefractive Information Storage Materials (PRISM) test stand for evaluating photosensitive samples. It also illustrates the fundamentals of a holographic storage system, as shown in the picture above

A blue-green argon laser similar to the one above is split into a reference and an object beam. The object beam, which is the carrier for the data is expanded to fully illuminate a spatial light modulator (SLM). What’s an SLM? It is an LCD panel that displays a page of binary data as a grid of pixels being either on or off.

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