GB2472031A - Multi-spectral holographic security marker using pressure sensitive material substrate - Google Patents

Abstract

A multi-spectral holographic security marker 2 comprises an image plane volume hologram recorded in a polymeric pressure and light sensitive film data carrier, with one hologram area a having a first replay frequency (wavelength) and one or more other areas b having a further, different replay frequency (wavelength); the different frequencies may be in the visible and invisible (ultraviolet (UV) or infrared (IR)) bands. A surface, pressure imprinted, hologram 3 may also be present. The different frequency response holographic areas may be formed by differentially compressing regions a and b, thus distorting Bragg planes (shown as curved lines); thus, even if initially recorded with a single volume hologram, different multi spectral regions may be formed by distortion, e.g. by means of a die (10, Figure 3). Security information carried by the marker is a combination of the size and shape of different colour/frequency replay areas together with the hologram content itself which is spread across the different replay areas.

Description

TITLE

Method for its Manufacture and Holographic Security System

Field of the Invention

Ihe mi cation relates to the field of holographic security marking and provides a multi-spectral holOgrahic security marker and system that ëreates a wide range of potenti tlly aluablc novel security marking opportunities, all svitli considerably enhanced security.

Background Art

Holographic security markers are cunently incorporated into a vide range of product'.

which have high intrinsic value or which contain personal or commercially sensitive information. Credit cards and many passports include holographic panels, as do many currency notes. Typically those holographic panels are surface holograms, otherwise known as relief holograms or holographic optical elements (i-lOBs) embossed into a surface of a portion, typically a metal foil portion, of the product which needs to be certified as genuine. Such HOEs are formed by the fonnation of a stuface diffraction grating on the foil. Typically the surface diffraction grating is embossed by pressing onto the toil a master negative' formed from a material haider than the metal of the foil. The press used is similar to a printing press.

it is known that volume holograms can include far more readabledata than surface holograms or HOEs. Their usc is however limited because the higher cost of creating volume holographic images currently outweighs the advantages. Voimne holograms have been proposed which replay in the visible rarge Volume holograms have also been proposed which replay in the mvibible range such as the intiared (IR) range Such an image is only properly displa cd vv hen mnterrogatud ii ith an appropriate beam which matches the recording beam in frequezicy and incidence angle, although it is known how to move the replay trequenci to another frequency, t\ pieall bi svelling oi contracting the substiate in tihich the hologram is recorded WO-A-2OO8IO4625 discloses the creation of a hologr'tphic security panci ot a high value article such a a mobile telephone in. which two volume holographic images are recorded in the same portion of the telephone casing One image is in the visible range of the spectrum and the oilier is in the invisible portion of the spectrum The volume holograms disclosed in WO-A-2008/045625 are however transmission holograms which when replayed generate an image in space ahoy e or remote from the recorded hot ographic film Ii v en if two volume holographic images are recorded in the sante secuut pant 1 as proposed above, they must be recorded separately and the accurac's of the registei of the two hologiaphic images is tlierefoie just as good as the accurac of the set-up of the initial recordings In main seem ity markers including those used to erify the genuine nature of bank notes one valuable aspect of the security guatantee is the accuracy of alignment of two or more elements of the printed oi holographic security markings. This invention seeks to provide a security marker and system in which a far higher degree of security is established by the accurate alignment of portions of a recorded volume hologram which have mutually different replay frequencies, optionally together with an equally accuiate alignment of those portion with elements of a surface reid hologram (ITOh) recoiding The Invention FIhe invention provides a muhi-spectral holographic security marker as defined in claim I herein! The marker incorporates a single volume hologram with at least two replay frequencies which preferably inchide frequencies in both the visible and invisible portions of the spectrum (for example bcth the visible and the JR range or both the visible and the UV range) the invention also provides a method of making such a holographic security marker as defined in claim 7 herein and a security system as defined in claim 14 herein! The holographic data in a volume hologram is contained in structures called "Bragg planes". Bragg's law and the Bragg condition are of importance for such holograms 2dsinO = XJn n -.3-where 0 is half the angle between the reference and the object beams at the recording stage (as well as the angle between the illuminating and the diffracted beams and the scattering planes in the emulsion at reconstiuction d i the spacing beusAecn the interference planes in thc enmlsion, X is thc wa clcngth in air and ii the average refractive index of the hologram medium.

The invention also preferably combines HOEs or surface holograms and the above multi-spectral image plane volume holograms in a unique maimer. Preferably the surface hologram of a security marker according to the invention comprises a visually recogmsable secmity image visible by the human eye without additional specialist hologram display and recognition equipment Such a hologram is commonly used in credit caids passports bank notes and packaging at present If in a seeurr marker according to the invention such a surface hologram were applied directly o'ver the portions of the image plane volume hologram capable of replay in the invi.sible part of the spectrum and between portions of the image plane volume hologram capable of replay in the visible part of the spectrum, then oii visual inspection one would see two aligned images. The image of the volume hologram would typically be viewable over a larger viewing angle than the surface hologram image and would he less sensitive to viewmg angle As the viewing angle changes, the surface holognun image will tend to vajy in colour or flicker, whereas the volume hologram image would be a more constant displa I he result ts ould be a very useful first order cheek on the genuine nature of the security marker. Misalignment of the surface and volume holographic images would immediately suggest a forgery By visual inspection the user can therefore immediately wiufy that the hologram displa\ed is tpical of ihat expected for the item being examined. Surface holograms of the Benton type display the effect of a rainbow whereas a volume hologram is seen as a single frequency replay.

Therefore if there were no variation in the appearance of the image then that would pro' ide an immediate visual indication to tl'e user that the ai tick being cxainincd w is not genuine ftc aligned surface hologram and at least that portion of the volume hologram beneath ieplavable in the isihle portion of the spectrum are preferably graphical in nature, for ease of recognition.

A far greater amount of data can however be contained in a volume hologram than in a surface hologram. One use of a security marker according to the invention could be for each volume hologram to include a digital code such as a bar code or a matrix code containing security data. Bar codes are sometimes referred to as unidimensional codes because they are.ssentialh imeai in data content There art. currently 28 difterent standards or symbologies, and typically bar codes would be read by a scanning laser. Two-dimensional or matrix codes are also known, and can contain far greater amounts of mformation or data Theie are currently 39 different accepted btandaids for matrix codes of which QR codes Quick Recognition codes) arc but one example Matrix codes cannot be iead by lascis as thcre is no established sweep pattern that can encompass the entire symbol 11ev are read by camera capture devices which are responsive to the complete two-dimensional matrix of each coded syiübol.

if the image plane volume hologram is recorded in the infrared ("1W') range and has a replay frequency in the JR range; and if parts of that image have been shifted into a isible ieplay frequency, then the entire image can only bc seen when tt is iiluminatcd by both an JR beam of the appropriate hequency and viewed at the appropriate angle and a visible beam of the appropriate frequcncy and viewed at the appropriate angle I herciore the holographic security s', stem of thc ins enuon preferably includcs a sccurity maiker volume hologram which is an image plane holographic recording of security information different parts of which are capable of display at diffeicnt vavclengths means for illunrinating the solume hologram with hght of those different wavelengths and a camera or data capture device able to identity and fuse together the different wavelength displays to recreate the complete security intormation The camcia or data eaptuic eqrupment can itself include a coded holographic key, so that if the volume hologram includes elements of a validation code or message (optionally distributed through the portions of the volume hologram ieplay able at diffeient frequencies and possibly through the surface hologiam as well) that code or message is readable only when matched with other elements of the same validation code or message included in th holographic key oi phase mask in the camera or data capture equipment. A simple validation code could he a word such as "GENUINE" or "VALID", individual letters of which or even individual pixels of which are distributed between the different portions of the volume hologram replaying at different frcquencics and optionally also betsseen the surface hologiarn and/rn the coded holographic key in the eamei a or data eaptui e equipment I he validation code would then only be ieadahle using the camera oi eata eaptuie cquipmcnt tuned to the actual frequencies of the different portions of the volume hologram. Consider also the sitUation in which the first volume hologram is a matrix code such as a QR code. Such codes can contain massive amounts of data, readable by a camera. To take advantage of the multi-spectral properties of the recorded hologram in which differcnt parts of the hologram replay at different tiequencies, that camera preferably rcads in both the \ miblc and an invisible fiequency range, and the image plane solume hologram contains portions ieadable in both ranges If that data is encrypted, then it can be sent to a computer for decryption only if a alidation code or message is read and recognized, that code or message being composed of data in the hologram and data in the camera filter or mask assembled to create the complete authorisation code or message recognized by the controlling software.

Volume Holqgamgqrdin Image plane volumc holograms can be recorded on ibm or thick film data carriers that aie sensitive to exposure to light to a rusolution that enables the cieation of inlonnaUon-carrying interference patterns For example the film data carrier may be a silver halide film having distnbuted therein nano-sized particles of photosensiuve matenal hrst, the film is exposed to create the information-carrying interference pattern. After exposure the information-carrying interference pattern is developed by techniques not dissimilar to know photographic development techniques, and after development the recorded interfeienee pattern is fixed in the data carner h removing from the film all nano-particles of the original unexposed photosensitive matenal As a generality the rcplay frequency of the recorded hologram is the same as the frequency of the laser which ereated the initial interference patterns within the film data carrier.

Photopqiyrsfp,lmage Plane \gjwnQFlo1ogran.ççgr4jflg The photopolymer volume hologram recording material used to record the image plane volume holograms according to the invention consists of three parts: a photopolymeniahle monomer an initiator system (which initiates pohnierization upon exposuie to light) and a polymer (the hindeñ A method to record an image plane volume hologram comprises first exposing the recording material to the information-carrying interference pattern. This exposure polymerizes a part of the monomer.

Monomer conccntration gradients, formed by variation in the amount of polymerwauon duc to the variation in cxposurcs, give ns to diffusion of monomer molecules from the regions ot high concentration to the regions of Ioser conccntrauon The process is simple and very suitable for mauhine processing Gtnerally the holograms ate reproduced by contact copying from masters (full hcarn copying 01 scanning hr a laser beam) The sensitivity of the polymer material resti iets the copying speed. The polymer material is more expensive than the niateridis currently used for creating surface or relief holograms, which is a reason why volume holograms are not gencrally used for security documcnts Despite that known cost detcn ent, howcvet, proposals do c\ist for inalung use of the higher security features as ailable from solunie holograms For cxaniple W02006i02 1102 discloses a possible combination of a i'olume hologram with a printed motif or even with a surface hologram to create a combined image, visible to the human eye, which indicates whether the item marked (which cotild be a bank note, a credit card or an identity card for example) is a valid item or not, Volume holographic data carriers ha c recently been de eloped which are both pressme-sensrtn e and light-sensitive They are polymers which, if they has c a volume hologram recorded on them can vary the display colour of that hologtam, dependent on the external pressure applied to the polymer Cuircntly the readih available pressure-sensitive and light-sensitive polymers are also cross-linkable. The replay frequency of the recorded hologram is fixed by the subsequent:eross4inking process. Cross-linking is usually achieved by ultraviolet irradiation. Therefore if the volume hologram is recorded on a film of such a polymer before cross-linking the colour of any display of that hologram can be varied and fixed by varying the external pressure applied during or immediately prior to the ultraviolet radiation which results in cross-linking of the polynrer. The variation of the colour of any display of the recorded hologram is a consequence of distortion of the Bragg planes of the data carrier material, which distortion is fixed when the polymeric material is cross-linked.

Thus cross-linking fixes the replay frequency, and therefore the colour (i.e. the wavelength), of the recorded hologram.

The recording of an image plane volume hologram in the above polymers is rather simple. The polymer film is generally laminated to a piece of clean glass or attached to a glass plate (or to some other pressure-resistant subsfrate) using an index-matching liquid.

Holograms can be recorded manually, but in order to produce large quantities of holograms, a special machine is required. For hologram replication a laser line scanning technique can provide the highest production rate. the photopolymer material typically needs an exposure of about 10 mJ/ctn2.

The creation of the optional surface hologram is initially carried out according to known procedures. A hard metal die is created, having embossed into its surface a surface diffraction pattern which is a negative of the diffraction pattern necessary to display the holographic recording. Such dies are conventionally used for the mass production of holographic security images on credit cards and batik notes, when they are pressed onto the surface of a foil clement of the item being marked, to create a positive impression which is the holographic diffraction grating. According to the invention, however, the die is made with two (or more) distinct thickness portions, preferably arranged in a rccognisable pattern. For example, thc die plate may have a basic constant thickness with an array of constant height studs extending from one face, to align together in another plane or in more than one other plane. The surface hologram negative is recorded only on the said one face, between the studs. The stud faces in that other plane or planes have not been recorded with the holographic negative. When the die is used to press the surface hologram into the top face of the photopolymer film which has the volume hologram recorded therein, or into a surface coating over that top face, the surface hologram is formed on the photopolymer film only on its top surface. and the array of studs causes compression of the photopolyrner film between the surface hologram recorded areas. Thus the volume hologram recordcd in the photopolymer film is coin cited into two or more portions of the same holographic image, replayable at diffeient frequencies The volume hologram portions recorded immediately below the surface hologram are either maintained at the original recorded replay frequency or moved to a minor extent to a higher replay frequency, and the volume hologram portions recorded below the studs are moved to a gieater extent to a higher replay frequmncy, caused by the greater compression of the photopolymer film beneath the studs If the studs are of heights terminating in iwo or mnoie planes thcn the portions of the volume hologram compressed by the studs of one height art moved to a different replay frequcnev than the portions compressed b studs of a different heigbL A conveise of the above geometrs is possible The surfaec hologram negative may be recorded only on the top surface of some or all of the studs of the die, so that in the final security marker the portion of the vohime hologram below the surface hologram has been moved to a higher replay frequency than the portion of the volume hologram below the aiea or areas not eanymg the suitace hologram diffraction pattern The surface holo grain impression die to he used in the i eeording of a security marker using time former geometry may for example be prepared by first cIeating a convuntional negative die of uniform thickness and having the surface hologram negative impression over the whole of its surface, then coating a. second layer of photoresist of a predetermined thickness on top of the surface hologram Then; an optical mask is utilised to image a pattein on top of the photoresist layer, causing alternating ateas of hardness when exposed to WV illumination This is then etched to i emove thi unexposed photoiesit theieb' revedling the surface iehef hologram below. This new pattern master wil he silvered and electroformed to create a new stamping die that now contains areas of smooth, thicker areas ("studs") and lower areas that have surface relief holograms to be used as a master die or stamper, achieving a precise depth to define the areas between the surface hologram impiessions in the final sccuuty marker film where the recorded volume hologram is shifted to a different replay frequency than the areas directly beneath the recorded surface hologram. &wing

Figure I is a schematic view of a security marker according to the invention; Figure 2 is a vertical section through the holographic security marker according to Figure 1; and Figure 3 is a perspective view of a die used to record the surface hologram on the security marker of Figure 1.

Figure 1 is a simple illustration of a security marker according to the invention.

Typically it comprises an image plane volume hologram of a specific image or pattern recorded at one frequency, for example visible grecn or invisible iR light. It has parts of its image shifted to a higher replay frequency, such as green to CV light which is invisible in the sense that it is no longer visible to the naked eye. or IR to visible light.

An optional surface hologram formed as a surface relief pattern hologram over the invisible replay frequency parts of the volume hologram adds an alteniating (channel) image to the remaining vicwable image. The invisible pattern is only discernible using suitable detection equipment and is needed to complete the security validation of the holographic elements of the sccurity marker when the multi-spectral (hyperspectral) nature of the complete security marker is analyzed.

The marker of Figure i consists of a holographic film data carrier 2 which has a general surface a of one height and circular depressions b of a lesser height. The portions b represent least one area of the display surface of the holographic film which has been compressed in a press, and the general surface a represents the remainder of the display surface. Of course, there may be other areas in addition, created by compressing portions of the film data carrier to different extents. As illustrated the portions b are discrete circles and the portion a is a continuous surface between and around those circular depressions b. It will he understood however that any combination of different shapes and areas can be contemplated, and indeed the -10 user can derive much information concerning the genuine nature of the security marker by close examination of the number, shape and distribution of the areas a and b in vshich the recorded holographic image aisplays in different speLtral banthvidths they may cusplay as differently coloured image portions or with onc portion being in the visible part of the spectrum and thc other being invisible to he hmnan eye For example the area a ina\ he directly over the part of an image plane volume hologram that has becn ieeordcd in the JR range in the film data caner 2 and which is rcplayable in the JR (invisible) part of the spectrum In contrast, the areas h he dnectl over and in fact define parts of the image plane volume hologram which have been compressed so as to distort the Bragg planes of the original recorded image plane volumc hologram and move the replay frequency into the visible range As an. optional security feature, the area a has hnpressed thereon a surface hologram.

Visually, the security marker of Figure 1 can be inspected by the naked eye, and it vii1 appear as a conventional surface hologram, for example a picture of an animal, symbol 01 othei logo which appears to move vhen viewed at different angles Ihe pattern of areas b however is of relativ dy Lonstant intensity and doe' not flicker as the vieving angle changes I he sc curny marker therefore has a distinctive appcaianee as an nidication of authenticity the rcgister betiseen the two images surfaee hologram and image plane volume hologram) is such that together they can be seen as complementary parts of thc same image fhe volume hologram does however contain much more potential data than does the surface hologram so a further secunty check can be by a closer s isual mnspcction of the hologiaphic display of the area a.

Not all of the recorded image plane v olumc hologram can however be seen through the areas b. Some has been recorded under the area a, hut that portion of the hdiographic recording has not had its replay frequency shifted to the visible part of the spectrum, and maintains a replay frequency in the JR range. That part of the image can be inspccied by illuminating the mmkei with JR light of the appropriate frequency and viewing the displayed image using an IR camera. Indeed, the apparatus for -11 -validating and reading data from the recorded hologram preferably comprises means for illuminating the security marker with both visible and invisible light of suitable wavelengths, and a dual frequency camera capable of image recognition in the visible and invisible ranges. To the uninformed observer such a camera detects only that hich is visible hut in ieahty it can iead thu visible portion ol the \ olume hologram beneath areas b together with the invisile portion beneath the area a. It can possibly aho read the surfacu hologiam image horn surface a Those images each contains a diffeient element of information contnbuting to the final merged or fused composite image which is detectable only by the camera If the cimera itself incorporates a coded holographic phase mask then dat r from all three (or potentially more) holograms together with data in the mask code is needed buibre the image can be validated.

Figure 2 shows at a very general and schematic level the construction of the security marker according to Figure 1 It comprics a support substrate 1 to which is adhered a holographic film data carrier 2. A volume hologram containing security data is recorded in the flint 2 A surface hologram 3is recorded on the portions of the film data carrier marked a in Figure 1, with the areas marked b being devoid of any recorded surface hologram material I Ire area directly beneath thu urface hologram recorded zone a is a poition of an nnage plane ohime hologram capable of replay when irradiated by Tight of a first mteri ogation wa elength, for example IR light and the area b beneath ever portion that is not recorded suth a surface hologram IS another portion of thu same volume hologram but is capable of replay only when irradiatcd by an intenogaung beam of light having a different wavelength br example light in the visible range The two replay ficquency areas are icspectrvely depicted In Figure 1 by mutually different sets of curved lines, those lines being intended to represent the Bragg planes within the holographic film, which are distorted in the areas b so that they no longer have the same characteristics as the original recorded Bragg planes beneath the areas a. Even though the film data carrier 2 may have been initially recoided with a single \ olume hologram, by distorting the Bragg planes in onLy one of the two areas a and li, or by distorting the Bragg planes in the two areas to different extents, there is provided according to the invention a multi-

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spectral security marker incorporating composite holographic information, in which the portions of the recorded volume hologram replayable at one frequency is aligned precise] y beneath the portions a of the security marker carrying the surface hologram 3, and the portions of the recorded volume hologram replayablc at the other replay frequency is confined precisely to the areas b directly beneath portions of the film data carrier which have no surface hologrmn recorded thereon.

Figure 3 illustrates how the security marker of Figure 1 is created. Initially the film data carrier 2 of Figure 1 is of uniform thickness throughout, and is a polymeric pressure-sensitive and light-sensitive material that is capable of volume holographic storage. An image plane vohtme hologram is recorded in that film data carrier. That initial recording may he in the visible or in the invisible part of the spectrum. The invisible parts of the spectnun include the lR and UV frequency ranges. initially the volume hologram is recorded over a specific and predefined area of the tUrn data carrier, typically but not exclusively the whole of its area. The surface hologram may then be created either directly on the exposed upper surface of that film data carrier or on a surface coating applied thereto. If the surface hologram is applied to a surface coating, then that surface coating must be one that is partially transmissive. The surface hologram is transferred in a press using a holographic die which has embossed into the surface thereof a negative of the surface relief required to generate the necessary interference fringes in the top surface of the film data carrier 2 to create the surface hologram. A suitable die 10 is shown in Figure 3. It has the same overall area as the predefined area of the film data carrier in which the volume hologram has been recorded. Most of the die 10 comprises a metal plate 11 of uniform thickness, but extending from one face of that plate 11 is an array of studs 13. Their thickness is somewhat exaggerated in Figure 3 for ease of illustration. The plate surface 12 between adjacent studs has embossed thereon the negative of the surface hologram, as illustrated schematically by diagonal hatching. The end faces of the studs 13 have no such surface hologram embossed thereon.

The die 10 can be used in a press similar to that used for the current creation of surface holograms used as security markers in credit cards and bank notes, among -13 -other items. in credit card and bank note security markers, the die is pressed downwardly onto the surface of a foil strip. According to the invention, the die 10 may he pressed down either onto the actual upper surfice of the film 2 in which the volume hologram is embedded, or onto a surface coating over the film 2 When the die 10 of I igure 3 is pressed onto the surface of the hoographic film 2 according to the invention the final suiface hologram or HOE is cmeated as an embossed diffraction grating on the surtace of the film 2 or of its coating only in the arca a shown in Figure 1, being the arta betieen the studs 13 of Figure 3 Ihe film area ii beneath thestuds 13 is compressed by a significantly greater amount. The compmcssion in the areas a may or may not he sufficient to distort the Bragg planes and to move the recorded volume hologram beneath the areas a to a different replay frequency. The film 2 beneath the areas b as defined by the studs 13 is compressed to a much gieatei amount, mesuhing in a cignificant distortion of the Bragg planes and a significant shift of the reply frequency of the olume hologram recorded in the film 2 beneath the aieas b Ii will immediately be seen that the resulting olunre holograms replayable at mutually different interrogation frequencies, are directly and precisely aligned with the portions a of the final film 2 which carry the HOE. Immediately after the pressing of the die 10 onto the film carrier 2, thefilm carrier 2 may be cross-linked if cross-hnking is necessary to maintain the distortion of the Bi agg planes I hat cross-unking may be achieved by exposure of the film 2 mnunedmatelv after the embossing proeess, to ulti am rolet radiation [he final replay frequency of mdrs idual areas of the vohime hologram is a function of the initial recording mm avelength Howcver the degree of momement of the volume hologram replay frequency in the zones b is also a function of the initial thickness of the holographic fllm 2, the axial extent of the studs 13, and the pressureused during the step of imprinting the surface hologram or HOE in the areas a. None of those three variables is readih ascertainable by any method of reverse engineeung according to which a forger might try to delaminate and inspect the security marker of Figure 1 [he creation of an identical security marker as a forged guarantee of authenticity of an article so marked is therefore mirtually impossible Other paiametci s which can affect th% dmtortion of the Bragg planes duming the impression -14 step when the die 10 is pressed against the surface of the holographic film 2 are temperature and humidity, and those also are parameters that are easy for a genuine minufacturer to control but impossible to ascertain even by destiuctu e examination of the resulting tharker.

The fusion of the shifted and the unshifted playback frequencies of the volume hologram in a marker according to the invention achieves a degree of security vastly superior to anything that could ha e been achieved in known manufacturing techniques Prior to this invention, the rceoidal of two volume holograms in a film data carrier replavctble at different excitation frequencies, has required two separate hologram reLoida! processes That is expensive and does not havc the accuraLv of the method of the present invention, which starts out with a single recorded volume hologram and then separates that into hologram portions with two mutually different replay frequencies. Furthermore it has never before been possible to achieve the exact register between the surface and multiple frequency volume holograms that is achieved according to the invention.

Thc holographic st curity marker of the in ention affords a number of discrete and independently veufiable levels of securuv At first glance the recorded HOE can be inspected visually if that is not the dc ice or symbol normally associated with the product to which the security marker is attached, then it can be assumed that the product is not genuine. A more detailed examination can detect whether the HOE and the volume hologram recorded in areas b are aligned accurately For cxampk the recorded holograms could incorpoiate a single line which continues from one hologiani to the other without interiuption, or could comprise cross hairs in one hologram which align viih a target device in the other either being a reasonable indication of security Alternatively the letters or pixels of a word indicating the getiuine nature of the article to which the security marker is attached could be divided between the FlOE and the volume hologram recorded in area b, so that the complete word can easily be read, but only when the two holograms arc in precise alignment, as they are according to the invention. -15-

A still further level of security can be achieved in a system which includes a hologram as descubed tho\ e in conjunction with a light source for exposing the hologiam iecorded in the area a to a ctimulating radiation outside of the visible range If the recoided hologram is then ieplayed at that ticquency outside of the visible range, then a special purpose camera or other equipment foE reading the image can be used to recognise every element of the recorded hologram. By comparing the elements of the recorded hologiam outside of the visible tange with the conesponding elements tecorded in the \ isible range and in particular by comparing the mutual alignment of those two holographic images, a fin ther guarantee of authenticity of the article Lnalked with the security marker can be obtained A final level of secunty can be ohta'ned if a volume hologiain tecorded in the holographic film directly beneath the.

areas b in Hgure I contains some but not all of a security code or number, and the camera or other reading equipment includes a holographic phase mask for adding dat r to that security code or number. Then a block can be established, preventing any encrypted data read from the \ olume hologram from being sent to a decryption computer until such time as a complete authorisation code has been identified. For ultimate security, that authorisation code could be split between all three recorded holograms in the security marker aceoiding to the in'centron and a hologiaphic phase mask or key contained within the camera.

An alternative conformation (not illustrated) of the die 10 of Figure 2 would be to have the negative of the holographic diffraction medium embossed on the otherwise planar ends of the studs 13 rather than on the surface bet een adjacent studs I he result would be that in Figure 3 the areas a would display only the volume hologram jn the fiequency range of the original iecording or a trequency close thereto (for example the JR range) and the aieas b would contain the HOE directly oer volume hologram iecordings capable of ieplav at a different frequency, for example a frequency in the visible range. -16-

Claims (5)

1. I. A multi-spectral holographic security marker comprising an image plane volume hologram recorded in a film data carner which is a p01) meric pressure-sensitis e mid hght-sensiti\e material that is capable of olume holographic storagu, wherein at kat one area of the hologram has a first ieplay frequency and one or more othei areas of the hologram each has a rcpIa frequency differing from the thst
2. 2. A security marker according to claim 1, wherein the one or more other areas of the hologram include areas with mutually different replay frequencies.
3. 3 A security markei accoi ding to claim I or claim 2 whcrem the areas of the hologram \hich hate different ieplav frequencies hae sharply dclmed boundaries which together form a security identification code or pattern.
4. 4. A security marker according to any preceding claim, wherein at least one of the replay frequencies is in the visible spectrum and at least one is in the invisible spectrum.

   S A scctu ny marker according to any pruceding claim, wherein a surface hologram is recordud on thu surface of the film data carrier or on a surface coating theieon, over thu said at least one aiea of the recorded volume hologram with the boundary or boundaries of the surface hologram coriesponding precisely with the boundary or boundaries of the said at least one area of the recorded volume hologram.

   6 A security markei according to any preceding claim itherein the image plane volumu holo,iarn recordccl in the film data carner comprises a linear odc or a matrix code containing security data.

   7 A method of m4king a multi-spuctial holographic security marker according to claim I tshich method comprises -17-recording, in a fihi data carrier which is a polymeric pressure-sensitive and light-sensitive material that is capable of volume holographic storage, an image plane voiumc hologram has ing a first replay flequcncy and covcring a predefined area of the film data carrier; preparing a die otte or more portions of which have a given thickness and one or more other portions of which have at least one thickness greater then the given thickness; and piessing the die into the surface of the fi1m data carrier or into a surface covering thereon the pressure being utficient to mote the replay flequencv of tht portion or portions of the volume hologram recorded directly beneath the portion or portions of the master die having the greater thickness to one or more other replay frequencies; thereby creating in the film data carrier an image plane volume hologram of which at least one area has the first replay frequency and at least one other areahas a replay frequency differing from the first.

   8 A method according to claim 7, wherein the first replay frequency of the oluine hologram is in the tnfraicd range and the replay frequency oi frequencies of the volume hologram in the one or more other areas is or are in the visible range 9 A method accordtng to chum 7, wherein the first replay frequency of the volumc hologram is in the %isible range mmd the replay frcqueiicy or fiequencies of the oluine hologram in the one or mon. other areas is or are in the ultraviolet range A method according to any of claims 7 to 9, wherein the die is a holographic master die, with one or more coplanar portions of a surface thereof carrying the negative of a surface diffiaction grating embodying a surface hologiam so that when the master die is pressed into the surface of the film data carrier or into a surface coating thereon, the pressure is sufficient to create, on the surface or surface coating, a surface hologram which is directly above and in precise alignment with an area or areas of the iecoidcd volume hologram which has the first repla', frequency -18 11. A method according to any of claims 7 to 9, wherein the die is a holographic master die, with one or more coplanar portions of a surface thereof carrying the negatne of a surface diffraction grating eniboding a surface hologiarn so that when the master die is pressed into the surface of the film data carrier or into a surface coatrng thereon the pressure is sufficient to create on the surface oi surface coating, a surface hologram which is directly above and in precise alignment with an area or areas of the recorded volume hologram which has a replay frequency differing from the first.12 A method according to claim 10 oi 11 wherein the surface hologiam is di ectly above and in precise alignment ith at least one aiea of the iecoided volume hologram which has a teplay fiequency in thc in isible spectrum 13 A method according to claim 12, wherein the surface hologram is directly above and in precise alignment with at least one area of the recorded volume hologram which has a replay frequency in the JR portion of the spectrum.la A secmit) system comprising a multi-spectral hologiaphic security maikei accordmg to claim I, wherein the security marker volume hologram is an nnage plane holographic recording of seem ity information parts of which are capable of display at different vavelengths, means for illuminating the volume hologram utb light of those diffeient wavelengths, and a multi-spectral camera or data capture device able to identify and fuse together the different wavelength displays to recreate the complete security information.A security system according to claim 14, vheiein a surface hologram is iecoided ovc't that part oi parts of a surface of the film data earner lying directly osei a part or parts of the recorded image plane volume hologram having a replay frequency in the invisible part of the spectrum.ió. A security system, according to claim 14 or claim 15, wherein the complete security information is encrypted in the \ oluin hologram recording and a fusion of the information present in the different wavelength displays, optionally together with information c)rltained in the suiface hologiam if present is needed to enable tL security information to be passed to a decryption program or device.17. A security system according to claim 16, wherein a fusion of the information present in the different wavelength displays, optionally together with information contained in the surface hologram if present, and together with information present in a holographic phase mask in the camera or data capture device is needed to enable the sccunty information to hi. passed to the decryption program ot deict iS A secunty system according to any of claims 14 to 17 wherein a fusion of the information present in the different wavelength displays, optionally together with information contained in the surface hologram if present, and together with information present in the holographic phase mask in the camera or data capture device5 causes generation of a visually recognisable word, phrase or sign indicating to a user that the security marker has been identified as genuine.Amendments to the claims have been filed as followsCLAIMS1. A multi-spectral holographic security marker comprising an image plane volume hologram recorded at a first replay frequency in a light-sensitive film data carrier; wherein the film data carrier comprises a polymeric material that is pressure-sensitive so that on compression the replay frequency of the recorded volume hologram is shifted away from the first replay frequency; characterised in that the image plane volume hologram recorded in the film data carrier comprises graphical data or a linear code or a matrix code containing security data; and different areas of the film data carrier have been compressed after recordal of the volume hologram therein, with the result that a plurality of different areas of the film data carrier have a plurality of different replay frequencies for the hologram recorded therein, with the different areas having boundaries which together form a security identification code or pattern which provides further security data.2. A security marker according to claim 1, wherein the different areas of the film data carrier which have been compressed after recordal of the volume hologram therein include mutually different areas which have been compressed to mutually different extents, with the result that the mutually different areas have mutually different replay frequencies for the hologram recorded therein, each of the mutually different replay frequencies being different from the initial replay frequency. S...* . 3. A security marker according to either preceding claim, wherein at least one of the replay frequencies is in the visible spectrum and at least one is in the invisible S...: spectrum. *.s. * I4. A security marker according to any preceding claim, wherein a surface :* hologram is impressed, on the surface of the film data carrier or on a surface coating * .. thereon, over areas of the security marker in which the recorded volume hologram has the same replay frequency, with the boundary or boundaries of the surface hologram corresponding precisely with the boundary or boundaries of the said areas of the corresponding precisely with the boundary or boundaries of the said areas of the security marker in which the recorded volume hologram has the same replay frequency.
5. 5. A security marker according to claims 3 and 4, wherein the surface hologram is impressed over areas of the security marker in which the recorded volume hologram has a replay frequency in the invisible part of the spectrum.6 A security marker according to claim 5, wherein the surface hologram is impressed over areas of the security marker in which the recorded volume hologram has a replay frequency in the IR part of the spectrum.7. A security marker according to claims 3 and 4, wherein the surface hologram is impressed over areas of the security marker in which the recorded volume hologram has a replay frequency in the visible part of the spectrum.8. A method of making a multi-spectral holographic security marker according to claim 1, which method comprises: recording, in the film data carrier, an image plane volume hologram having the first replay frequency, being a hologram of graphic data or a linear code or a matrix code containing security data; preparing a die one or more portions of which have a given thickness and one or more other portions of which have at least one thickness greater then the given thickness, the boundaries of the different thickness portions of the die together forming a security code or pattern; and pressing the die into the surface of the film data carrier or into a surface :.: : covering thereon, the pressure being sufficient to move the replay frequencies of the portions of the volume hologram recorded directly beneath those portions of the die * having the greater thickness or thicknesses to one or more replay frequencies each different from the first replay frequency; *..*.S * * thereby creating in the film data carrier an image plane volume hologram of the linear code or matrix code security data, of which at least one area has the first replay frequency and at least one other area has a replay frequency differing from the first, with the different areas having boundaries which together form the said security identification code or pattern which provides further security data.9. A method according to claim 8, wherein the first replay frequency of the volume hologram is in the infrared range and the replay frequencies of the volume hologram in the plurality of other areas are in the visible range.10. A method according to claim 8, wherein the first replay frequency of the volume hologram is in the visible range and the replay frequencies of the volume hologram in the plurality of other areas are in the ultraviolet range.11. A method according to any of claims 8 to 10, wherein the die is a holographic master die, with one or more portions of a surface thereof carrying the negative of a surface diffraction grating embodying a surface hologram, so that when the master die is pressed into the surface of the film data carrier or into a surface coating thereon, the pressure is sufficient to create, on the surface or surface coating, a surface hologram which is directly above and in precise alignment with an area or areas of the recorded volume hologram which has the first replay frequency.12. A method according to claim 11, wherein the surface hologram is directly above and in precise alignment with at least one area of the recorded volume *, hologram which has a replay frequency in the JR portion of the spectrum.* ** *** * 13. A method according to any of claims 8 to 10, wherein the die is a holographic .: master die, with one or more portions of a surface thereof carrying the negative of a surface diffraction grating embodying a surface hologram, so that when the master die * . is pressed into the surface of the film data carrier or into a surface coating thereon, the * pressure is sufficient to create, on the surface or surface coating, a surface hologram * ** .S.* which is directly above and in precise alignment with an area or areas of the recorded volume hologram which has or which have at least one replay frequency differing from the first.14. A security system comprising: a multi-spectral holographic security marker according to any of claims I to 3; means for illuminating the volume hologram with light of different wavelengths corresponding to the replay frequencies of the different defined areas of the security marker; and a multi-spectral camera or data capture device able to identify and fuse together the different wavelength displays to recreate the complete security information.15. A security system according to claim 14, wherein a surface hologram is impressed over that part or those parts of a surface of the film data carrier lying directly over a part or parts of the recorded image plane volume hologram having a replay frequency in the invisible part of the spectrum.16. A security system according to claim 14 or claim 15, wherein the complete security information is encrypted in the volume hologram recording, and a fusion of the information present in the different wavelength displays, together with information present in a holographic phase mask in the camera or data capture device, is needed to enable the security information to be passed to a decryption program or device. S... * . *SSS17. A security system according to claim 16, wherein a fusion of the information * S55S0 * present in the different wavelength displays, together with the information present in L: * the holographic phase mask in the camera or data capture device, causes generation of a visually recognisable word, phrase or sign indicating to a user that the security marker has been identified as genuine. S. * * . S * *5 * **S* 1 8. A security system comprising: a multi-spectral holographic security marker according to any of claims 4 to 7; means for illuminating the volume hologram with light of different wavelengths corresponding to the replay frequencies of the different defined areas of the security marker; and a multi-spectral camera or data capture device able to identify and fuse together the different wavelength displays to recreate the complete security information.19. A security system according to claim 18, wherein a fusion of the information present in the different wavelength displays, together with information contained in the surface hologram, and together with information present in a holographic phase mask in the camera or data capture device, is needed to enable the security information to be passed to the decryption program or device.20. A security system according to claim 19 wherein a fusion of the information present in the different wavelength displays, together with information contained in the surface hologram, and together with the information present in the holographic phase mask in the camera or data capture device, causes generation of a visually recognisable word, phrase or sign indicating to a user that the security marker has been identified as genuine. S..' * * **5**** * * * *. * . S *. * S.. * S * . * * .*I * S.. I *