Optical: systems and elements – Holographic system or element – Having particular recording medium
Patent
1990-04-06
1991-09-03
Dzierzynski, Paul M.
Optical: systems and elements
Holographic system or element
Having particular recording medium
359 12, 359 33, 359900, G03H 120, G03H 122
Patent
active
050447084
DESCRIPTION:
BRIEF SUMMARY
The invention relates to holography and makes it possible to obtain particularly attractive representations, both because of the exceptional quality of the impression of relief obtained, and because of it has a particularly wide visual field.
A hologram is a recording, on a holographic recording material, of rays of light reflected by an object illuminated by coherent light.
Upon its reconstruction, by observing the holographic recording material illuminated in the way it was illuminated at the time of recording, the observer then sees the representation in relief of the object, in the region where it was located relative to the holographic recording material when it was recorded.
Depending on whether the ray of light reflected by the object and the ray of light directly illuminating the holographic recording material arrive at this material on the same side or on two opposed sides, the hologram is a transmission hologram or a reflection hologram.
At the time of the reconstruction, the observed image is called "real" when the observer perceives it in front (or on the near side) of the holographic recording material, and "virtual" when the observer perceives it behind (or on the far side of) the holographic recording material.
The space in which the real images appear is accessible to observers, who are able to place their hand where the image is located--an almost supernatural sensation. Contrarily, the space in which the virtual images appear is inaccessible, because it is located behind the holographic recording material, and obviously one's hand cannot pass through that.
Of course, there are also images that have both a real portion and a virtual portion, which is highly favorable to the effect of depth of field; the image of the object represented is thus particularly spectacular when the object itself has an elongated shape, such as the hull of a boat seen from the bow.
Furthermore, the term "orthoscopic images" is used for real or virtual images that reconstruct a normal relief, while "pseudoscopic images" are the real or virtual images that reconstruct a inverted relief: The convex portions at the time of recording are reconstructed as concave, and vice versa. A pseudoscopic image of a statuette, for example, would give the observer the impression at the time of reconstruction that he is looking at an open mold. Because it is contrary to nature, this makes an irritating visual impression.
To make a hologram, two operations are necessary; for good understanding of the invention they must be clearly distinguished from one another, even though they are actually inseparable, since they are both indispensible and they cooperate in producing to the final effect. The first is recording onto the holographic recording material, and the second is reconstruction, in order to present the holographic recording material, suitably illuminated, to an observer.
The quality of the reconstruction clearly depends on the quality of the recording, but to give an observer a strong sensation of reality, one essential condition is the span of the field of vision, in other words the value of the angle within which one or more observers must be located to perceive all the portions of the reconstructed image in relief. The field of vision is accordingly involved in the reconstruction, but not in the recording.
Nevertheless, the very nature of holograms means that both recording and reconstruction are highly intimately dependent on one another.
For example, in classical photography it is possible to take an image 24.times.36 mm in size and make copies in quite different sizes (up to 4.times.3 m for posters); in holography, this is impossible, because reconstruction can be done only on the same scale as recording.
Research into quality has therefore studied the operations of both recording and reconstruction.
E. P. Supertzi et al, in the article, "Wide-angle holography", in JOURNAL OPTICAL SOC. AM., Vol. 56, No. 4, April 1966, pp. 524-525, described a process with which the field of vision can be enlarged upon reconstruction of
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Optical Soc.Am., vol. 56, No. 4, Apr. 1966, E. P. Supertzi et al.: Wide-Angle Holography, pp. 524, 525.
Applied Physics Letters, vol. 8, No. 6, 15 Mar. 1966, F. B. Rotz et al.: "Holograms with Nonpseudoscopic Real Images", pp. 146-148.
Proceedings Intern. Soc. for Optical Engineering, SPIE 761,1987, SPIE (Washington, U.S.), S. A. Benton: "Alcove" Holograms for Computer-Aided Design, pp. 53-61.
Dzierzynski Paul M.
Lerner Martin
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