Method for production of holographic master - originals

The present invention relates to holography and is intended for the production of master holographic originals by pulsed lasers.

TECHNICAL LEVEL

Holograms are widely used for document and product authentication and as exclusive, authentic visual products. There are two stages in the hologram authentication process - user authentication and authentication by experts. As a result, authentic holograms always have features that allow both users and experts to recognize the authenticity of such a hologram. All of these features are first displayed on a hologram called a master holographic original, and then its diffractive structure is transmitted or stamped. , used directly in the production of embossed holograms (for Practical Holography, Third Edition, Graham Saxby; Taylor & Francis 2003, p. 328-333), or copied by contact as described e.g. WO 2009035310 (Lithuanian Patent LT5573), (for reflection holograms), or the holographic master-original itself can be used as an exclusive product

Thus, the production process of the holographic master-original is very important and its improvement is a pressing task.

One of the main image protection features of the holographic master-original is the 3D or 2D-3D image itself and the micro image seen with special optical equipment. Currently, such means are rendered in transmittance holographic master-originals by computing the desired diffraction grid using computers and recording it either in two intersecting coherent laser beams, either modulated by a spatial light modulator, or by photolithography or electron beam on a photosensitive material ( Ex: AV Goncharski, AA Goncharski Computer Optics & Computer Holography, Moscovv University Press, 2004.). Therefore, the photosensitive material forms a diffractive structure which, when illuminated, produces a holographic image and, by special means, a secret image. The holographic master-originals thus produced have all the features of a permeability hologram, viz they are visible by illuminating them from the opposite side of the view and have a rainbow color distribution or are seen as a color image in a narrow field of vision;

or is visible as a black-and-white image.

Protective reflection holograms are nowadays mostly produced by copying a holographic master-original with images of small real objects. (Optical Document Security by Rudolf L. Van Renesse; Books on Demand, 1994). Since prior to the present invention there was no known way of imaging the features of reflection in holograms with visualization, special reflective holograms are now rarely used for product and document authentication.

Known state-of-the-art transmittance holographic master-originals require sophisticated computational computing, and the exposure of photosensitive material itself takes from several to tens of hours. The state-of-the-art methods of recording reflective holographic master-originals cannot incorporate the visual features visible into the image only with the help of special optical equipment.

US Patent No. 7,747,992 discloses a method of producing holographic master-originals, wherein the unexposed photosensitive material is applied to the substrate simultaneously illuminated by focused coherent pulsed laser light modulated radiation and unmodulated coherent laser light (reference) radiation when the light is modulated so that element due to coherent modulated and unmodulated laser beam interference, the whole would reproduce a holographic 3D and / or 3D-2D hologram image.

These features are also exhibited by the method of producing holographic master originals described in patent application KR20070072772.

Meanwhile, from the Lithuanian patent no. The 4842 family (US7423792, US7800803) is a known class of digital holographic printers capable of capturing large format (A5 to lxl, 5m) digital image holograms with a high depth of field print and significantly accelerating the process of producing digital holograms. In this holographic master-original production method, the light modulator is illuminated by a spatial image formed by pixels taken from corresponding hundreds of 3D scenes, the light modulator is illuminated by a coherent pulsed laser light beam, and modulated radiation is focused by a special lens having an optical angle a photosensitive material is placed immediately behind the fold. The photosensitive material is illuminated by a pulse of modulated light, together with an unmodulated support beam of laser radiation, and a small holographic optical element (HOE) is incorporated into a small area of ​​photosensitive material known as the holopixel or hogel. After chemically or otherwise treating the photosensitive material and illuminating the HOE light recorded in a manner identical to that of the unmodulated laser light at the time of recording, the HOE will "project" the same spatial light modulator image from several hundreds of view the scene so that only one pixel image is projected in each direction.

Covering the entire surface of a photosensitive material with such HOEs, their whole behaves like a regular hologram - that is, slightly different parallax-linked images of the same 3D scene are seen at different angles of view and the viewer perceives the material as three-dimensional. Digital holograms recorded in this way require relatively little computation and are produced by pulsed lasers, which significantly speeds up the production of digital holograms.

Typically, digital image holograms recorded in this way are reflection holograms (ie, illuminated by the observer), although Lithuanian patent no. 4842 (or U.S. Patent No. 7,800,803) mentions the possibility of writing throughput holograms in this manner. However, transmission and reflection protective holograms made from the resulting digital hologram, the holographic masteroriginal, while having a spatial imaging depth that is not available in other spatial imaging holograms, would have only one feature of protective holograms, a 3D or 2D-3D holographic image. fully used for document and product authentication and as authentic visual products.

This patent from Lithuanian patent no. The known method of manufacturing master-originals 4842 is the closest to the present invention.

The object of the present invention is to improve the method of recording digital holograms so that along with the 3D and / or 2D-3D image, the digital hologram has other features of visual authentication that are only visible with the help of special optical equipment. In this way, the digital holograms thus produced could be used as holographic master originals for the production of embossed and reflective protective holograms, or the holographic master original itself could be used as an exclusive product and have a shorter production time than other known holographic master originals. time.

THE SUBSTANCE OF THE INVENTION

The object is achieved by a method of applying unexposed photosensitive material to a substrate while simultaneously illuminating with focused coherent pulsed laser light modulated radiation and unmodulated coherent laser light (backing) radiation, where the modulated light is modulated by holographic optical elements. modulated and unmodulated laser interferences, the whole would reproduce a holographic 3D and / or 3D-2D hologram image. What's new is that when illuminated with focused coherent pulsed laser light modulated radiation, it places a stealth imaging element in the light beam path before the modulator and selects its location relative to the optical rotation of the lens so that the streaming imaging element changes coherent laser light intensity in photosensitive material at the point of inscription of the holographic optical element, thus forming in said holographic optical elements the micro-image visible along with the hologram image by means of special optical equipment (lens, microscope, etc.).

If the exposed pixel and then the modulated coherent pulsed laser radiation and the unmodulated coherent pulsed laser radiation intersect at the same side of the photosensitive material, it records the transmittance holographic master-original.

If the exposed pixel and then the modulated coherent pulsed laser radiation and the unmodulated coherent pulsed laser radiation intersect at the opposite sides of the photosensitive material, it records the reflection holographic master-original.

The photosensitive material can be illuminated by multiple color coherent pulsed laser beams simultaneously or sequentially.

The secret imaging element may be a liquid crystal reflection or transmittance display or slide, or an image thereof may be used, broadcast to a selected location as above, so that its image is focused on the photosensitive material. Video streaming or image transfer can be used.

Other objects of the invention are the master original produced by the method of the present invention and a hologram with a recorded covert image produced from such master original.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a proposed holographic master-original recording scheme for transmission and reflection master-origin recording (top view), it is clear to those skilled in the art that, instead of a skipping surround light modulator, the present scheme may be modified to operate with a reflective surround light modulator.

FIG. 2 shows an example of an image transmitted in a surround light modulator during recording of a single holographic optical element in the case of a holographic master-bandwidth transmission.

FIG. 3 shows an example of an image illuminated by a spatial light modulator during recording of a single holographic optical element in the case of a reflection holographic master-original.

FIG. 4 shows an example of an image transmitted in a secret imaging element during recording of a single holographic optical element in transmission and reflection in holographic master-originals.

FIG. Figure 5 shows how holographic optical elements cover a desired area of ​​photosensitive material.

EXAMPLE OF IMPLEMENTING THE INVENTION

The proposed method may be implemented by the device shown in Figs. 1. It consists of a light source pulsed laser 1, a semi-transparent mirror 2 positioned along its beam path, which distributes the light flux to an objective reflection from the mirror 2 and a support beam passing through the mirror 2. The objective luminous flux through the mirrors 3 is transmitted through a scatter-focusing module 4, a secret image-forming element 5 (which may also be part of a scatter-focusing module), a collimating lens 6, a modulator 7, a special lens 8, (e.g. lens, analog similar to that described in Lithuanian Patent No. 4,842 (or U.S. Patent No. 7,880,803 to the same family) having an optical fold on its exterior, where a light-sensitive material 10 applied to a solid or flexible substrate 11 is placed immediately behind the fold. The reference light flux is transmitted by the mirrors 12 through a beamformer 13 which forms a support beam transmitted by the mirrors 14 from the same transmittance on the same side of the photosensitive plate in the master-record 15 or from the opposite side of the photosensitive plate in the case of the master-record. a beamformer 13 so as to illuminate an area close to the area of ​​the photosensitive material, 9. The shape of a normally illuminated area is a rectangle, although it should be clear to one skilled in the art that the illuminated area may also be in the shape of another regular polygon.

The substrate 11, on which the photosensitive material 10 is applied, may be transparent in transmittance master-original recording and opaque in reflection in master-original recording, is placed on computer controlled sliders which slope it in directions 17 and 18 (direction 18 is vertical in Figure 1). plane) (computer controlled sliders Fig. 1 not shown).

The proposed method is implemented by this device in the following order.

The unexposed photosensitive material 10, applied on a solid or flexible, transparent or, in the case of a master-original of holographic transmittance, a possibly opaque substrate 11, is placed on a slider in computer controlled directions 17 and

18th (direction 18 is vertical to the plane of Fig. 1) (computer controlled sliders Fig. 1) to illuminate two coherent laser beams: objective beam 9 and support beam 15 (in the case of transmission holographic master-original production) or support beam 16 (reflection beam) in the case of master-original production).

The mirrored coherent beam of pulsed laser light reflected through the system of mirrors 2 and 3 passes through a light-sensitive layer through a scattering-focusing module 4, a secret imaging element 5, a collimating lens 6, a modulator 7, a lens 8, which becomes a focused and modulated objective light beam 9 10. The spatial light modulator 7 illuminates an image to form a holographic optical element, an example of which is illustrated in FIG. 2 (in the case of bandwidth master-original) and Figs. 3 (for reflection master-original).

The secret imaging element 5 illuminates the image by varying the intensity of the coherent laser light radiation which forms the visual authentication features in the holographic optical element, an example of which is shown in FIG. 4. The position of the secret imaging element 5 is selected such that the lens 8 focuses the illuminated image of the modulator 7 on the photosensitive material 10 at the point of insertion of the holographic optical element, thereby forming a micro-image visible with said hologram image in said holographic optical elements.

Meanwhile, the unmodulated coherent pulsed laser radiation from the mirror system 2, 12 passing through the beamformer 13, at the I position of the reflecting mirror 14, reaches the photosensitive material on the same side as the objective beam when recording the transmitting holographic master5 original or reflecting mirror 14 II. position accesses the photosensitive material from the opposite side when recording the reflection holographic master-original.

During exposure, the photosensitive material 10 is uniformly moved in direction 17 such that after each pulse of laser radiation, it passes a distance equal to the edge of the illuminated surface of the reference radiation in the scrolling direction (when its illuminated area is rectangular). When the illuminated area of ​​the reference beam is of regular polygonal shape, the photosensitive material shall, after exposure, be at a distance equal to the lateral direction of the rectangle into which the polygon may be enclosed.

By exposing one row in the direction 17, the photosensitive material is shifted in the direction 18 at a distance equal to the edge of the illuminated surface of the reference radiation in the direction of scrolling (when its illuminated area is rectangular); when the illuminating area of ​​the reference beam is of regular polygonal shape, the photosensitive material is displaced at a distance equal to the edge of the rectangle to which said polygon may be enclosed; and sequentially exposing, as above, FIG. 5, which shows a coating of a holographic masteroriginal surface with holographic optical elements that will form a microscope, visible with a magnifying glass or microscope, along with a hologram image.

Next to the stealth imaging element 5, the coherent laser radiation from the laser 1 is introduced by mirrors 3 and the semi-transparent mirror 2. It should be clear to a person skilled in the art that the laser radiation can be led to the coherent laser radiation scattering and focusing module 4 that the stealth imaging element can also be placed inside the scatter focus module.

Shape beams 15 and 16 are formed by a beamformer so that they illuminate in the photosensitive area an area close to that of the objective beam 9. Normally, the illuminated area is rectangular in shape, although it should be apparent to one skilled in the art that of regular polygon shape.

Mirrors 14 are used to direct the formed support beam to the photosensitive material (it should be apparent to one skilled in the art that the formed laser beam may also be directed to the photosensitive material using a different mirror arrangement).

The coherent laser radiation is transmitted from the laser 1 to the beamformer 13 by means of mirrors 12 (it should be apparent to a person skilled in the art that the laser beam may be directed to the beamformer 13 also by other mirror arrangement).

The objective / support beam ratio can be varied by using, for example, waveguides and polarizers mounted anywhere in the beam path (Fig. 1 not shown).

The master-original obtained by the method of the invention is characterized in that each 3D imaging holographic optical element (holopixel or hogel) contains a secret image, which is visible by special optical means (magnifying microscope).

The digital holograms thus produced can be used as holographic master originals in the manufacture of embossed and reflective protective holograms, or the holographic master original itself may be used as an exclusive product.

Tests have shown that the proposed method enables you to record e.g. 25x30mm master-originals with deep 3D holographic imaging in 20 minutes, while advanced master-hologram recording equipment - electron beam master-hologram recording - would produce a similar, but not so deep, master-original for at least 24 hours [ AV Goncharski, AA Goncharski Computer

Optics & Computer Holography, Moscow University Press, 2004.]. In addition, the electron beam master hologram recording equipment is unable to achieve the 3D depth of the master master original in the proposed mode.

Thus, the proposed method of recording master holograms not only enables the production of a deeper 3D image master image compared to the closest known one, but also incorporates micro-text or secret image visible with special optical equipment, which significantly improves the user and security features of the master holograms. -original made according to the proposed method.