RU2168197C2 - Process of generation of iridescent holographic images - Google Patents

Abstract

FIELD: technical physics. SUBSTANCE: proposed process differs from traditional method of generation of impressed iridescent holograms by effect of aberration of optical systems recorded on hologram as object and visualized with the aid of test objects, for instance, objects-transparencies, diaphragms or lattices. EFFECT: simplified realization of process. 2 dwg

Description

 The invention relates to technical physics and is intended to protect against counterfeiting of critical documents and securities, application in advertising and applied art based on holography.

 A known analogous method of obtaining rainbow holographic images is that a hologram is produced by the optical method, after which the resulting hologram is replicated on thin-film media, which are then applied to documents protected from forgery [1].

 The disadvantage of the analogue method is the comparative simplicity of forgery of holograms made in accordance with it at the modern level, even in small private enterprises.

 There is a known prototype method for producing rainbow holographic images, which consists in the fact that a hologram of a discrete set of wave fields carrying information about several phases of the object’s motion is produced by electronic photolithography, the resulting hologram is replicated on thin-film media, which are then applied to documents protected from forgery. When the position of the head of the observer looking at the hologram is shifted, images of the object in various phases of its movement fall into his eyes, which is perceived by the observer as a discrete movement of the reconstructed image [2].

 Using the prototype method, holograms are produced that restore a larger, in comparison with the analogue, number of images of objects such as thin lines — trajectories of circular or elliptical orbits or patterns. Forging such holograms is much more difficult than those described above.

 The disadvantage of the prototype method is the high cost of the necessary equipment and the complexity of its operation.

 The essence of the invention lies in the fact that in the method of obtaining rainbow holographic images, which consists in producing a rainbow hologram of a discrete set of wave fields that carry information about several phases of the object’s movement, the resulting hologram is replicated on thin-film media, which are then applied to documents protected from forgery , the effect of the aberrations of optical systems recorded on a hologram as an object is visualized using test objects, for example, transparency objects, apertures, or and gratings.

 The invention is illustrated in FIG. 1 and 2. In FIG. 1 shows one of the options for obtaining a hologram according to the proposed method. The notation in FIG. 1 along the propagation of illuminating radiation 1: 2 - a lens with aberrations (such as a condenser), 3 - an opaque screen with a horizontal moving hole 4, 5 - an auxiliary test object, 6 - transparency photograph of a visualized (positive) image of operations, 7 — recording medium for obtaining a hologram; 8 — converging reference wave field. Figure 2 shows the image restoration scheme of one of the replicated holograms sprayed with a reflective coating: 1 - a restoring source of ordinary white light, 2 - a hologram, 3 - a vision zone, which is a reconstructed composite image of a slit blurred into a rainbow, 4 - eyes of an observer.

 According to the proposed method, radiation 1 of a laser operating in a single-mode or single-frequency mode illuminates a lens 2 having aberrations and shielded by an opaque screen 3 and a further test object 5 (diaphragm or grating) located to visualize the wave field transmitted through the open portion of the lens. Depending on the type of aberrations after visualization, they can take the form of circles, ellipses, hyperboloids, etc. A rendered image of aberrations corresponding to different positions of the hole 4 is photographed and placed positive photos 6 sequentially in front of the recording medium 7, which also sends the reference wave field 8. The hologram is recorded by successive exposures, and between them the hole 4 is shifted in the horizontal direction by an amount approximately equal to its length plus two lengths restored its source, since the reduction takes place convolution functions describing the opening and the source function, every time the banner photo-setting with the corresponding aberrations visualized image to protect against radiation exposure reference portions of the recording medium is not illuminated object radiation. After receiving the hologram, it is replicated on thin-film media, which is then applied to the protected documents in accordance with the well-known conventional technology.

 The reconstructed image is observed by illuminating the hologram 2 with the white light source 1, while the reconstructed image of the slit hole obtained by successive recordings on the hologram of the hole 4 is blurred in the vertical direction into the rainbow, forming a vision zone 3 in which the eyes of the observer 4 are located. When moving the eyes of the observer 4. in the horizontal direction in front of it, various visualized images of aberrations are sequentially restored, which is perceived by the observer as their discrete change of.

 In the horizontal direction, the size of the vision zone is determined by the diameter of the lens 2 only when restoring the slit hole in a 1: 1 scale. However, by choosing the distances between the hologram and the centers of curvature of the reference and restoring wave fields that are unequal to each other, you can restore the slit hole with any desired magnification and obtain the necessary viewing area, respectively.

 Aberrations can also be visualized by interference methods, including shear ones, then the visualizing test object is no longer necessary, but the hologram production scheme will be somewhat more complicated, since it will be necessary to introduce an additional visualizing reference wave field.

 Another option for visualizing the effect of aberrations is that a test object is recorded on the hologram, which looks like a positive image on a transparent basis / like a slide /, which is called a transparency object in holography. An optical system having, for example, spherical aberrations, the transparency focuses at a distance of several centimeters from the recording medium onto which the hologram is recorded. The effect of aberrations is manifested in the fact that on a reconstructed image a flat object-transparency is observed as spherical, rotating when the direction of observation changes. Note that such an action of aberrations differs significantly from those considered in classical optics. Indeed, it considers the intensity of the image obtained, averaged over the entire aperture of the optical system. In this case, information on the observer’s eyes is not about the intensity, but the wave fields themselves, which passed only through individual zones of the optical system and were not averaged over the entire aperture.

 Experimental verification of the proposed method confirmed the significant / compared to the prototype / simplicity of its implementation with more diverse visual capabilities of the obtained holograms.

Sources of information
1. N.G. Vlasov. Rainbow holography. Nature, 1993, N 8, p. 74-80.

 2. Holographic Optical Security Systems Pros. Of SPIE, 1991, v. 1509, p. 67-72.

Claims (1)

 The method of obtaining rainbow holographic images, which consists in producing a rainbow hologram of a discrete set of wave fields that carry information about several phases of the object’s movement, replicating the resulting hologram on thin-film media, which are then applied to documents protected from forgery, characterized in that the optical aberrations systems recorded on the hologram as an object, visualized using test objects: transparency objects, or apertures, or gratings, the hologram is recorded vayut successive exposures and between them is displaced in the horizontal direction of the aperture in an opaque screen designed for screening the lens having aberration.

Images