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Holographic Memory

Holographic Sensors




2. “Holography (from the Greek ὅλος hólos, "whole" + γραφή grafē, "writing, drawing") is a technique that allows the light scattered from an object to be recorded and later reconstructed so that when an imaging system (a camera or an eye) is placed in the reconstructed beam, an image of the object will be seen even when the object is no longer present. The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the image appear three-dimensional.

The holographic recording itself is not an image; it consists of an apparently random structure of either varying intensity, density or profile.

Holography is a technique that enables a light field, which is generally the product of a light source scattered off objects, to be recorded and later reconstructed when the original light field is no longer present, due to the absence of the original objects.[19] Holography can be thought of as somewhat similar to sound recording, whereby a sound field created by vibrating matter like musical instruments or vocal cords, is encoded in such a way that it can be reproduced later, without the presence of the original vibrating matter.

Holograms are recorded using a flash of light that illuminates a scene and then imprints on a recording medium, much in the way a photograph is recorded. In addition, however, part of the light beam must be shone directly onto the recording medium - this second light beam is known as the reference beam. A hologram requires a laser as the sole light source. Lasers can be precisely controlled and have a fixed wavelength, unlike sunlight or light from conventional sources, which contain many different wavelengths. To prevent external light from interfering, holograms are usually taken in darkness, or in low level light of a different colour from the laser light used in making the hologram.

Holography requires a specific exposure time (just like photography), which can be controlled using a shutter, or by electronically timing the laser.

A hologram can be made by shining part of the light beam directly onto the recording medium, and the other part onto the object in such a way that some of the scattered light falls onto the recording medium.

A more flexible arrangement for recording a hologram requires the laser beam to be aimed through a series of elements that change it in different ways. The first element is a beam splitter that divides the beam into two identical beams, each aimed in different directions:

 One beam (known as the illumination or object beam) is spread using lenses and directed onto the scene using mirrors. Some of the light scattered (reflected) from the scene then falls onto the recording medium.

 The second beam (known as the reference beam) is also spread through the use of lenses, but is directed so that it doesn't come in contact with the scene, and instead travels directly onto the recording medium.

When the two laser beams reach the recording medium, their light waves intersect and interfere with each other. It is this interference pattern that is imprinted on the recording medium. The pattern itself is seemingly random, as it represents the way in which the scene's light interfered with the original light source — but not the original light source itself. The interference pattern can be said to be an encoded version of the scene, requiring a particular key — that is, the original light source — in order to view its contents.

This missing key is provided later by shining a laser, identical to the one used to record the hologram, onto the developed film. When this beam illuminates the hologram, it is diffracted by the hologram's surface pattern. This produces a light field that is identical to the one originally produced by the scene and scattered onto the hologram. The image this effect produces in a person's retina is known as a virtual image.”

(Wikipedia, Holography, 6/7/2012)


1. “Research into development of new data storage devices is fueled by the continuing demand for ultra-high information capacity, more data density, and faster readout rates. Conventional data storage techniques rely on storing information bit by bit on the surface of the recording medium. The two-dimensional storage techniques, however, are rapidly reaching their fundamental physical limits beyond which individual bits may be too small to easily inscribe or read. A promising alternative approach is holographic data storage, in which information is stored throughout the volume of the storage medium. The key challenge in the field of holographic data storage is the development of a suitable storage material that meets all the stringent requirements.

Despite intensive research effort, suitable and commercially viable holographic material still remains illusive. In holographic data storage, a complete page of information is recorded as an optical interference pattern created by two intersecting laser beams within a thick photosensitive material. The interference pattern of these two coherent writing beams induces a periodic change in the refractive index of recording material. Though there are a number of photochemical reactions that can be utilized to achieve the refractive index modulation, very few exhibit quantum yields greater than unity. Nonlinearity of the photochemical reaction is essential to the required high sensitivity and hence ultrafast recording speed of the storage media. Photopolymerization is such a nonlinear reaction and hence utilized in fabrication of leading holographic media. However, a number of issues limit the performance and commercial viability of photopolymers. Major issues include shrinkage of the material due to formation of new bonds and diffusion of the monomers, polymerization inhibition due to oxygen and other inhibitor included in formulations to impart long shelf life to the media, induction period and need of pre-exposure due to inhibitors, dynamic range reduction due to pre-exposure, low shelf/archival life and several others. Hence, there is significant unmet need for a high performance holographic media.”

[Hawker et al, US Patent 8,187,770 (5/29/2012)]


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(RDC 6/5/2012)


Roger D. Corneliussen

Maro Polymer Links
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Copyright 2012 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen

* Date of latest addition; date of first entry is 6/7/2012.