Optical: systems and elements – Holographic system or element – For producing or reconstructing images from multiple holograms
Patent
1992-04-02
1993-08-10
Arnold, Bruce Y.
Optical: systems and elements
Holographic system or element
For producing or reconstructing images from multiple holograms
359 1, 359 28, G03H 126
Patent
active
052354423
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for the recording and the visual restitution of a tridimensional scene by means of a coherent light source.
Such methods are known and are called holographic methods. Fringes resulting from an interference between a reference beam and the diffuse light coming from the scene are recorded on a photosensitive plate. During the restitution, the holographic plate is illuminated by a coherent source, and the image of the scene can be observed behind the hologram. Here, the visual range of the scene depends on the observation angle and on the distance at which observation takes place.
The invention intends to present a method of photographic recording and visual restitution of a scene allowing to reconstitute the visual field of the scene during restitution independently of the distance from which it is observed.
The invention uses a phenomenon which M. Francon has described in a book "La granularite laser (speckle) et ses applications en optique", edition Masson 1978. This speckle phenomenon observed on a photographic plate inscribed by a coherent source is generally considered as an annoying and inconvenient phenomenon. That is why it is eliminated as far as possible both in photographic and in holographic assemblies. It has been found surprisingly that by illuminating by a coherent source only a very narrow element of the surface of the scene during recording, there are recorded, on a photographic plate and in the form of speckles, all the informations not only concerning this element but also concerning all objects illuminated in a secondary way. In fact, these objects too receive the diffuse light and retransmit it towards the environment.
The invention will now be described more in detail means of three figures.
FIG. 1 shows diagrammatically the configuration between a coherent source, the scene and the photographic plate during recording.
FIG. 2 gives the aspect of a photographic plate such as it is visible after recording of a scene,
FIG. 3 indicates diagrammatically the configuration between the coherent source, the photographic plate and the observer during visual restitution of the scene.
With reference to FIG. 1, there is to be seen a coherent light source 1 constituted by a laser which emits a fine beam 2 towards an object 3, the image of which is to be recorded. The diameter of the beam 2 is voluntarily very reduced, for example some tenth of millimeters, and illuminates thus a very small portion of the scene 3. A photographic plate 4 is disposed to receive the light reflected from the scene 3. A screen 5 serves to avoid the direct passage of the light between the laser 1 and the photographic plate 4.
As a function of the roughness of the scenic element hit by the beam 2, a more or less large quantity of the energy of the coherent beam is diffused towards the other parts of the scene and towards the environing space. It is then observed that the photographic plate is printed in a very particular way. There are in fact to be seen (see FIG. 2) more or less dark spots of variable sizes and of a distribution which seems at a first glance equally random. This phenomenon is called a speckle.
It has to be noted here that there is a fundamental difference between classical holograms and the speckles according to the invention. In fact, up to now, it has been tried to uniformise as far as possible the beam illuminating the scene in order to illuminate all the portions of the scene in the same way. Here, on the contrary, the incident beam is concentrated as much as possible in order to obtain an intensity distribution which is as heterogenous as possible. Consequently, it is no more the whole scene which receives the incident light, but a very small portion of this scene.
By taking a photographic plate 4, inscribed as shown in FIG. 2, and by illuminating this plate 4 by a coherent light source 6, an observer 7 finds that the light is diffracted after having traversed the plate and reconstitutes the entirety of the original tridimensional scene. During observation of this imag
REFERENCES:
patent: 4717221 (1988-01-01), McGrew
patent: 4783133 (1988-11-01), Chen
patent: 5138471 (1992-08-01), McGrew
P. Harihan "Optical holography: Principles, Techniques and Applications", 1984, Cambridge University Press, ISBN 0521243483.
Applied Optics, vol. 27, No. 12, Jun. 15, 1988, (New York, US), M. Trivi et al.: "Three dimensional display through speckle patterns: a single exposure method", pp. 2370-2371.
Applied Optics, vol. 22, No. 6, Mar. 15, 1983, (New York, US), H. J. Rabal et al.: "Stereograms through a speckel carrier", pp. 881-885.
Franchi Marco
Grossetie Jean Claude
Arnold Bruce Y.
European Economic Community
Ryan J. P.
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