HOLOGRAPHIC BACKGROUNDS

Abstract: A method of holographing an object wherein, in order to obtain a required diffusely illuminated background, the object is holographed against a background constituted by a hologram which is adapted to simulate a real background from which the hologram has been produced. Typically, the object is holographed against a hologram of a matt white box. The background hologram is preferably a hologram used in its pseudoscopic mode but may be a hologram used in its orthoscopic mode but projected as a real image.

Description: Holographic Backgrounds This invention relates generally to holography and more specifically to a method of obtaining a diffusely illuminated background in single beam reflexion holography It is a common practice, in order to obtain a diffusely illuminated background when producing a holo¬ graphic image of an object using the single beam technique to place the object in an open matt-white rigid box. However, this commonly used known method is not entirely successful, primarily for two reasons. The first is that a very limited number of multiple reflection can occur before the light is beyond the coherent length o a typical laser. The second is that a relatively high proportion of the laser light, reflected from the walls of the box, becomes unfavourably polarised with respect to the light initially incident on the holographic plate. It is an object of this invention to provide an improved method of obtaining a diffusely illuminated back¬ ground in single beam reflexion holography. According to the invention, in order to obtain the required diffusely -illuminated background, the object to be holographed is placed in front of a background con¬ stituted by a hologram used to simulate a real background from which t e hologram has been produced. The background hologram is preferably a hologram used in its pseudoscopic mode. Used in its pseudoscopic mode, the background hologram presents a real image as the background for the object being holographed, but an image which is an inside-out version, analogous to a mould, of the original object. Thus, a matt white box illuminated from the exterior appears in the background hologram as a white box diffusely illuminated on the interior. However, an analogous effect is achievable wherein a hologram is used in its orthoscopic mode but projected as a real image. In this case the background hologram is made from a hologram of the original background. Thus, the original background can be a box made of ground glass, illuminated from the exterior. A hologram made of this box would present a virtual image if used as background, and would therefore be of little value, but a second hologram made of the first hologram will present a real image if used in its orthoscopic mode as the background for the object to be holographed. In general therefore, the method of the invention, whilst resultir.σ in a final holograph of an object as though the object was placed in the real background environment, e.σ. a matt-white box, gives an improved final holograph because the previously mentioned dis- advantages of the known method are substantially avoided. OMPI « o An example of the method of the invention will now be given. In this method, a truly bright split beam hologram of a cube with a matt white surface is produced. The sides and top of the cube are made as evenly bright as possible, and the hologram thereof produced is of the reflexion type obtained by incidence of the reference beam from below. The hologram is processed to give it a peak response under the laser light to be used. The hologram produced as above described is then employed in its pseudoscopic mode aε a background to diffusely illuminate an object placed in front of it. A holograph of such an object, produced using normal sinσle beam overhead reference, will appear as if it had been placed in a matt-white box. Clearly, other hologram shapes can be used to form the illuminated background, according to circumstances. For example, multiple beam illumination of a white hemisphere will produce a hologram which, when viewed pseudoscopically, will give the effect of a real back¬ ground in the form of a bright hollow shell. An object placed in front of such a hologram can be holographed by the Denisyuk single beam technique. Although the object will cast a shadow on the area of the hologram behind it, this effect is not substantial enough to be materially disadvantageous provided the background hologram is larger, preferably appreciably larger, than the object. A modified method requires the production of a first hologram from which a second hologram is made to constitute the background for the object being holographed. For example, a ground glass box is illuminated from the outside and holographed, and €hen a second hologram made from the first is used in its orthoscopic mode as the background which acts for diffuse illumination of the object being holographed.

Claims: Clai s 1. A method of holographing an object according tc which, in order to obtain a diffusely illuminated back¬ ground, the object to be holographed is placed in front of a background constituted by a hologram which simulates a real background from which the hologram has been produced. 2. A method according to claim 1, wherein the back¬ ground hologram is used in its pseudoscopic mode. 3. A method according to claim 1, wherein the back- ground hologram is used in its orthoscopic mode, being a hologram produced from a hologram of the real background. 4. A method according to any of claims 1 to 3, wherein the object is holographed by the Deniεyuk single beam technique. 5. A method according to any of claims 1 to , vr.erein the background hologram is a holcgrs of an illuminated open-sided matt white enclosure. 6. A method according to claim 5, wherein the object is holographed as if positioned in the matt white enclosure, and is therefore diffusely illuminated. 7. A method according to claim 3, wherein the first produced hologram is a hologram of an enclosure made of a translucent material and illuminated from the outside. 8. A method according to claim 7, wherein the translucent material is ground glass. 9. A method of holographing an object substantially as hereinbefore described.

Inventors: BLYTH JEFFREY, BLYTH, JEFFREY
Applicants: APPLIED HOLOGRAPHICS, APPLIED HOLOGRAPHICS PLC
Application year: 1984
Main classification: G02B5
IPC codes: G02B5, G03H1