MXPA01000079A - Methods and apparatus for rendering an optically encoded medium unreadable - Google Patents

Abstract

Methods and apparatus are provided for making an optically readable media (20) unreadable. The method includes steps of (a) providing the media (20) with an optically activated mechanism that degrades the reflectivity of a surface wherein information is encoded;(b) exposing the media (20) to optical radiation for reading out the information;and, during the step of exposing, (c) initiating the operation of the optically activated mechanism. In a further aspect the optically activated mechanism causes a defocusing of a readout beam, thereby degrading reflection of the readout beam from a surface wherein information is encoded. In another embodiment the method deforms a surface of the layer resulting in readout beam aberration or in an inability to correctly stay on track. In another embodiment a portion of the surface is removed to the atmosphere, such as by evaporation or sublimation.

Description

METHODS AND APPLIANCES TO MAKE AN OPTICAL ENCODED ENVIRONMENT ILLEGIBLE CLAIMING THE PRIORITY OF A COPENDIENT PROVISIONAL PATENT APPLICATION With this, priority is claimed under 35 U.S.C. §119 (e) of co-pending provisional patent application 60 / 090,682 filed on 6/25/98. The description of this provisional patent application is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION This invention relates to optically readable data storage media and, more particularly, to techniques for rendering said media illegible after it has been read at least once.

BACKGROUND OF THE INVENTION It is often desirable when distributing software or other information that is registered in a medium, to ensure that only one group can read the recorded information. For example, a company that sells computer software will discover that it is advantageous to allow only the buyer to read the software from a disk and transfer or install the software to computer memory, such as a hard disk, while avoiding subsequent access by others. groups to software. However, this has shown that it is an annoying problem that has not yet been resolved. When the information is distributed over a reading / writing medium, such as the ubiquitous soft disk, it may be possible for the installation software to erase all or part of the information after it has been installed successfully. Unfortunately, said information can be distributed on protected write disks, thus making said deletion impossible. In addition, any protection mechanism that relies on computer software to be implemented has the potential to be overridden by additional computer software. The patent of E.U.A. 5,815,484 discloses an optical disk having a reflective metallic layer with a plurality of data structures (pits and flat regions) and a reactive compound superimposed on at least some of the data structures. The reactive compound is a photochromic compound that changes from an optically transparent condition to an optically opaque condition when subjected to reading light and / or atmospheric oxygen. The darkening of the photochromic compound prevents a sufficient amount of reading light from being detected by the reading apparatus, thereby rendering the optical disc illegible.

At least one perceived disadvantage of this method is that the photochromic dimming is often reversible, which could be used to override the technique.

OBJECTS OF THE INVENTION It is a first object and advantage of this invention to provide an improved system and method for rendering an optically readable medium, such as, but not limited to, a laser disk, a compact disc (CD) or a digital video disc (DVD), readable. It is a second object and advantage of this invention to provide an improved system and method for rendering a permanently illegible, optically readable medium, after it has been read at least once. It is a third object and advantage of this invention to provide an optically activated mechanism that destroys or impairs the reflectivity of a metal-containing layer, thereby rendering it readable to an optically readable medium. It is a further object and advantage of this invention to provide an optically activated mechanism that modifies a transparent layer so as to cause aberration of the read beam, thereby rendering it unreadable to an optically readable medium. It is a further object and advantage of this invention to provide a mechanism that relies on non-atmospheric oxygen, such as oxygen pre-charged into or generated within a layer of an optically readable medium, to modify the optical properties of the medium to return to the medium optically illegible. It is yet another object and advantage of this invention to provide a mechanism that relies on a technique of evaporation to modify the optical properties of an optically readable medium so as to render the medium optically readable. It is another object and advantage of this invention to provide a mechanism that alters a surface characteristic of an optically readable medium such as to detrimentally affect a scanning method of a reading device during an attempt to read the medium. It is a further object and advantage of this invention to provide a mechanism that causes changes in the surface topography to an optically readable medium such as to detrimentally affect a scanning and feedback method of the reading device., thereby adversely affecting the accuracy of the reading.

BRIEF DESCRIPTION OF THE INVENTION The aforementioned and other problems are overcome and the objects and advantages of the invention are realized by methods and apparatus according to embodiments of this invention.

In one aspect this invention provides a method for rendering an optically readable medium illegible during an execution procedure. The method includes the steps of (a) providing the medium with an optically activated mechanism that degrades the reflectivity of a surface on which information is encoded; (b) expose the medium to optical radiation to read the information; and, during the exposure step, (c) initiate the operation of the optically activated mechanism. In this embodiment the step of initiation includes the steps of (d) generating singlet oxygen in a layer disposed on the medium; and (e) reacting the singlet oxygen with a metal-containing layer to oxidize the surface of the metal-containing layer, thereby degrading the reflectivity of the surface. The generation step may include a singlet oxygen diffusion step through a diffusion barrier that is disposed between the layer and the metal-containing layer. In a further aspect the optically activated mechanism causes a defocusing of a read beam, thereby degrading the reflection of the read beam from a surface on which the information is encoded. In one embodiment, the method generates an optical intensity gradient in a layer disposed on the medium; and, in response to the generated gradient, it deforms a surface of the layer that results in aberration of the read beam and / or adversely affects the tracking procedure, resulting in reading degradation and loss of fidelity. In this case the step of providing provides the layer as for understanding a polymer containing azobenzene. In an alternate embodiment a surface layer may react with an atmospheric component, such as oxygen, to degrade the screening process by inducing a change in surface topography, without inducing any significant change in the light transmission properties of the surface layer. In another embodiment the step of initiation includes the steps of: irradiating a photocurable polymer region comprising part of the medium; and, in response to irradiation, photopolymerize the polymer, thereby changing a refractive index of the polymer resulting in aberration of the reading beam. This invention also encompasses optically encoded media that operates in accordance with the methods mentioned above, and which are constructed in accordance with the techniques of this invention. According to further embodiments of this invention, an optically readable medium has a pattern-like structure for encoding information that can be read by applying light, and additionally includes a layer that is composed of a volatile component and at least one other component . Removing some of the volatile component by evaporation or sublimation causes an increase in at least one of photoabsorption or dissipation with the remaining component, thereby rendering at least a portion of the encoded information illegible. The other component may include a lactone ink, such as crystal violet lactone, and the volatile component may be, for example, NMP (N-methyl pyrrolidone). In a further embodiment an organic material, such as CsF or KBr, is coated on the surface of the disk and provides a surface haze when exposed to water vapor or carbon dioxide, thereby increasing the dissipation and decreasing the ratio of signal to noise, and degrading the reading fidelity. A method for rendering an optically readable medium illegible is described. This method includes the steps of (a) providing the medium with a surface layer having a flat surface topography; and (b) subsequent to or during a first reading of the optically readable medium, modify at least a portion of the flat surface topography to a non-planar surface topography. This is achieved by using at least one of a photoresponsive polymer, a removal of a substance from the surface layer to the atmosphere, or by interaction with a substance in the atmosphere. This latter method can occur without significantly modifying a transparency capability of the surface layer to a reading beam. The deviation of the non-planar surface layer topography from the flat surface layer topography is sufficient to detrimentally affect at least one scanning operation of a reading device that generates the read beam.

BRIEF DESCRIPTION OF THE DRAWINGS The features set forth above and others of the invention become more apparent in the following detailed description of the invention when read in conjunction with the accompanying drawings, in which: Figure 1 is a schematic diagram of an optical scanning system conventional for reading an optically readable disc incorporating one or more features of the present invention: Figure 2 is a schematic view in lateral elevation and in partial cross section of an optical scanning head of the optical scanning system scanning the optically readable disk of FIG. 1. FIGS. 3A and 3B are a first pair of partially enlarged cross-sectional views showing a portion of the optical disk of FIG. 2 according to a first embodiment of the invention, specifically a layer modality of FIG. optically deformable photopolymer, in which the portion of the disc is shown in the figur 3A and 3B both before and after, respectively, scanning by an optical beam. Figures 4A and 4B are a first pair of enlarged partial cross-sectional views showing a portion of the optical disc in Figure 2 according to a second embodiment of the invention, specifically a modification mode of optically induced reflectivity. , in which the portion of the disk is shown in Figures 4A and 4B both before and after, respectively, scanning by an optical disk. Figures 5A and 5B are a first pair of enlarged, partial cross-sectional views showing a portion of the optical disc in Figure 2 according to a third embodiment of the invention, specifically an optically cured photopolymer modality, in which the portion of the disc is shown in Figures 5A and 5B both before and after, respectively, scanning by an optical beam. Figure 6 is a flow chart plotting the generation of singlet oxygen in a photosensitizing layer of the optical disc shown in Figure 2, according to the reflectivity modification mode shown in Figures 4A and 4B. Figure 7 illustrates a colorless lactone form (crystal violet lactone) and its cationic (color) form, and is useful to explain an embodiment of this invention that uses an evaporative method to render an optically readable medium readable; and Figure 8 is an enlarged cross-sectional view of a portion of an optically readable medium having a surface topography that is modified from a flat profile, and which can be used to detrimentally affect the operation of tracking the device. reading according to the teachings of this invention.

DETAILED DESCRIPTION OF THE INVENTION Referring next to Figure 1, there is shown a schematic diagram of an optical scanning system 1 for reading an optically readable disc incorporating one or more features of the present invention. Although the present invention will be described with reference to the embodiments shown in the drawings, it should be understood that the present invention can be realized in many forms of alternate embodiments. In addition, any suitable size, shape or type of materials or elements could be used. It should further be noted at the outset that as used herein an "optically encoded" or "optically readable" means or media is designed to cover a number of various devices in which data, audio and / or video information is stored from way that can be read when a ray of light, (either visible light or non-visible light) is applied to the device. Such devices include, but are not limited to, laser discs, compact discs (CDs), CD-ROMs, and digital video or versatile discs (DVDs), as well as certain types of tape. In general, the devices of interest to this invention incorporate some type of structure that is capable of altering the reflectivity of the device to the reading light so that a logic bit 1 can be distinguished from a logic bit 0. Upon return to said "illegible" device should be understood that it is not necessary to make the entire device completely illegible. For example, it may be necessary to make only a relatively small portion of a load record or an unreadable content directory so that the entire device becomes unusable, or so that some predetermined portion of the device becomes unusable. Making the device illegible may also encompass adversely affecting the feedback and optical tracking procedure of the reading device, such as by altering the surface topography. For example, in this case the focus settings of the reading laser may not be able to react quickly enough to changes in surface profile, resulting in an inability to maintain the correct tracking. This has been discovered to manifest itself as "jumps" through a segment of music on a compact disc, or in some other way negatively impacts the fidelity of the output. The optical scanning system 1, which may be conventional in construction, generally comprises a disk drive 10 and an optical scanning head 30. The disk drive 10 is generally adapted to move an optically readable disk 20, such as a CD-ROM, in relation to the optical scanning head 30. In the embodiment shown in Figure 1, the optical scanning head 30 is located below the optical disc 20 to scan a lower surface of the disc, although in other embodiments The scanning head can be located to scan a top surface of the disk. The scanning head 30 is preferably held by a drive or movable arm (not shown) so that the head 30 can be moved relative to a center of the disk.

For example, the scanning head may be capable of moving radially relative to the center of the disk 20 or circumferentially around the center of the disk. In alternate embodiments, the optical scanning head can be held fixed relative to the center of the optically readable disk. As the disk 20 moves on the scanning head 30, the head reads optically readable data structures 23 (see FIG. 2) disposed on the disk 20. Referring still to FIG. 1, the disk drive 10 includes a motor 12. , a drive shaft 14 and a disk or sleeve holder 16. The drive shaft 14 operably connects the motor 12 to the sleeve 16. In this way, when it has power the motor 12 rotates the sleeve 16 through the drive shaft 14. The sleeve 16 comprises suitable fastening means (not shown) for stably holding the disc 20 therein when the sleeve 16 is rotated by the motor 12. The motor 12 is adapted to rotate the sleeve 16 and the disc 20 held in the same at predetermined speeds. The motor 12 can operate to rotate the disk 20 at a variable rotational speed so that the disk presents a reading surface to the scanning head 30 moving at a constant linear velocity. For example, as the scanning head 30 moves radially closer and closer to the center of the disk 20 on the sleeve 16, the motor 12 rotates the disk 20 at a speed of rotation that increases. In this way, the portion of the disk 20 passing over the scanning head 30 moves at a constant linear velocity. It is noted that in conventional laser disks, the data structure is generally arranged in a single spiral track from the edge of the disk towards the center which requires the disk to rotate at a variable speed of rotation in order that the track move at a constant linear velocity in relation to the scanning head. By way of example, the disk impeller 10 can rotate a DVD at a rotational speed that is suitably increased to provide a linear velocity of about 3.5 m / sec on the scanning head 30. With reference to FIG. 2, the scanning head 30 generally includes a light source 32 and a photodetector 34. The light source 32 generates and directs an incident or interrogation beam 100 of electromagnetic radiation (also referred to herein as optical radiation) against the optical disk 20. The optical disk 20 includes a reflective layer 22 with data structures 23 formed thereon or the same. The interrogation beam 100 of electromagnetic radiation directed against the optical disk 20 is reflected by the reflective layer 22 as a reflected beam 102. The reflected beam 102 is then detected by the photodetector 34 of the optical scan head 30. When the impeller disk 10 rotates disk 20 in relation to scanning head 30, interrogation beam 100 passes over data structures 23 on reflective layer 22 of the disk. As the interrogation beam 100 moves over the data structures 23, the data structures modulate the reflected beam 102. The modulation in the reflected beam 102 is recorded in the photodetector 34 of the scanning head 30 and converted to electrical signals More particularly, and by way of example, the light source 32 may include a laser diode 36 or another such suitable device for generating the interrogation beam 100 of optical radiation. The beam 100 generated by the laser diode 36 can be directed through a quarter-wave plate 40 and through a polarization beam splitter 38 as shown in Figure 2. Alternatively, the positions of the plate The waveguide and the ray fractionator can be reversed so that the beam first passes through the beam splitter and then through the wave plate. further, the beam generated by the laser diode 36 can be collimated by a collimator (not shown) before finding the wave plate 40. After the interrogation beam 100 passes through the beam splitter 38, the beam encounters a suitable lens 42 which focuses the interrogation beam 100 to a predetermined focal point. The interrogation beam 100 emitted by the light source 30 may have a wavelength of about 650 nm, although the beam may have other wavelengths. The interrogation beam 100 can be focused to a point size of approximately 0.63 μm. The focus depth of the beam 100 is approximately 0.9 μm although this depth can be adjusted as required. The interrogation beam 100 is modulated by a suitable modulator (such as an acoustic or electroacoustic optical modulator, not shown) to effect a residence time per bit of between 100-200 nsec. The laser diode 36 is adapted in another way to supply approximately 1 mW of energy on the optical disk 20. The energy deposited per bit by the interrogation beam 100 is approximately 200 pJ and the influx of the beam on the focusing point is approximately 50 mJ / cm2. Therefore, the intensity of the interrogation beam 100 on the focus point is approximately 300 kW / cm2. In alternate embodiments, the light source may have any other suitable configuration for generating an interrogation beam of electromagnetic radiation having suitable characteristics for reading data structures of an optical disk. Still with reference to Figure 2, the reflective layer 22 of the laser disk 20 is disposed between an upper protective layer 24 and a lower layer 26. The construction of the lower layer 26 will be described in greater detail below with reference to the three embodiments preferred of this invention. The reflective layer 22 may be comprised of metal such as aluminum, although other suitable materials may be used, and which is formed by suitable means to provide a reflective surface 28 to the interrogation beam 100. As mentioned above, the reflecting surface 28 of the layer 22 is encoded with stored information such as data structures 23. The data structures 23 are adapted to change the reflected beam 102 when the interrogation beam 100 impinges on characteristics of the data structures 23. For example, the structures of data 23 may comprise a pattern of flat regions 25 and pits 27 formed in the reflective surface 28 of the optical disk 20. The flat regions 25 are raised portions on the reflecting surface 28 of the optical disk. The holes 27 are sunken portions (relative to the flat regions 25) on the reflective surface 28 of the optical disk 20. For example, the individual holes 27 can have a width of approximately 0.4 μm and a length of approximately 0.4-1.9 μm, although the holes can have any other suitable length and width. In alternate embodiments, the data structures formed on the reflective surface of the optical disk may have any other suitable characteristics that change a reflected beam quality when the interrogation beam encounters those characteristics. By way of example, said characteristics may be sequences of scarified and reflecting surfaces or through holes in the reflecting surface of the optical disc. In the preferred embodiment, as shown in Figure 2, the interrogation beam 100 generated by the light source 32 is focused by the lens 42 so that the focal point is located on the "background" surface of the holes. on the reflective surface 28 of the optical disk 20. When the interrogation beam 100 impinges on the surface of a hole 27, the interrogation beam 100 is reflected by the hole surface as a reflected beam 102. The reflected beam 102 passes through. of the lens 42 (which now acts as a collimator for the reflected beam) and is then deflected by the beam splitter 38 to strike the photodetector 34 in the scanning head 30. When the interrogation beam 100 is directed instead to a region flat 25 of the reflecting surface 28, a smaller amount of the ray 100 is reflected back to be detected by the photodetector 34. This is because the surface of the planar region 25 is located at a different depth than the focus depth of the interrogation beam 100. Alternatively, the interrogation beam 100 generated by the light source can be focused by the lens to the surface of the flat regions 25 and not to the holes 27. In any case, it can be seen that the change in reflectivity between two states (corresponding to whether the interrogation beam 100 impinges on a hole 27 or on a flat region 25) provides a mechanism for encoding binary data (ie ones and zeros) on the surface of the disk. Preferred embodiments of the present invention will now be described only with reference to the case where the interrogation beam 100 focuses on the surface of the holes 27 in the reflective surface 28 of the optical disk 20, although the teachings of this invention are equally applicable to the case where the interrogation beam focuses instead on the surface of the planar regions 25. With reference to FIGS. 3A and 3B, there is shown an enlarged cross-sectional view of a portion A of the optical disk 20 according to FIG. with a first embodiment of this invention. The optical disk 20 is constructed to include a layer of surface relief photopolymer 200. The surface relief photopolymer layer 200 is comprised of one or more polymers, such as, for example, a polymer containing azobenzene. It is known that a polymer containing azobenzene is capable of exhibiting a surface deformation in response to the presence of an optical intensity gradient. Reference in relation to this can be had to an article entitled "Gradient force: The mechanism for surface relief grating formation in azobenzene functionalized polymers", Applied Physics Letters, Vol. 72, No. 17, pps. 2096-2098, April 27, 1998, J. Kumar et al. The authors report on the derivation of a model for the formation of holographic surface relief grids in functionalized azobenzene polymers. The forces that lead to the migration of polymer chains with exposure to light in the absorption band of an azo chromophore are attributed to dipoles that interact with the gradient of the electric field present in the polymer material. The authors also report that efficient trans-cis cycling in azobenzenes allows cooperative movement of chromophores under the influence of gradient forces. In accordance with the teachings of this invention the surface relief photopolymer layer 200 is disposed on the optical disk 20 so that the interrogation beam 100 passes through the layer 200 when the beam 100 interrogates the data structures 23 on the reflective layer 22 of the optical disk 20. The surface relief photopolymer layer 200 in this case forms the lower layer of the optical disk 20. A surface 201 of the photopolymer layer 200 is interfaced on an adjacent layer of the disk 20 and the opposite surface 202 of the photopolymer layer is a free or unrestricted surface (see FIG. 3A). In this preferred embodiment, the surface relief photopolymer layer 200 is deposited by suitable methods (eg spray or spin distribution) directly against the reflecting surface 28 of the reflective layer 22 on the optical disk 20. In alternate embodiments, the The surface relief photopolymer layer can be deposited on an intermediate substrate between the reflective layer of the optical disc and the photopolymer layer, so that again the photopolymer layer has an unrestricted surface. Figures 3A and 3B show respectively the surface relief photopolymer layer 200 in an initial or non-deformed condition, before exposure to interrogation beam 100., and then in a deformed condition after exposure to interrogation beam 100 (Figure 3B may not be a scale drawing). The surface relief photopolymer layer 200 is exposed to the interrogation beam 100 when the optical disk 20 is scanned by the optical scanning head 30 (see also Figure 2). As shown in Figure 3A, when the optical disk is first scanned and the surface relief layer 200 is in a non-deformed condition, in interrogation beam 100 it is focused to penetrate through the surface relief layer 200 and to be reflected as a reflected beam 102 from the surface of the holes 27. In this manner, the disk can be read in the normal manner as described above. However, exposure of the surface relief photopolymer 200 layer to the interrogation beam 100 also causes a deformation 210 on the unrestricted surface 202 'of the photopolymer layer 200, as shown in Figure 3B. The deformation 210 projecting outwardly in the photopolymer layer 200 changes an amount of polymer material through which the beam must travel and, at least due to the fact that this additional material has a refractive index that differs from the air, the interrogation beam 100 experiences lightning aberration, resulting in a blurring of the interrogation beam. This defocusing is sufficient to cause a change in the amount of reflected light that is received by the photodetector 34, and thus to cause at least one portion of the disk to be read incorrectly, which is the desired result. As such, errors are generated in subsequent attempts to read the optical disk. It has been observed that the surface relief deformations, created optically or by the evaporation mechanism of this invention, of at least a few hundred nanometers, may be sufficient to cause an optical disk to become illegible, or to decrease Significantly, reading fidelity due to reading problems induced by reading ray tracking. More particularly, the interrogation beam 100 generated by the light source 32 of the scanning head 30 (see Figure 2) is focused to penetrate through the non-deformed surface relief photopolymer 200 layer and form a size of less than, for example, 1 μm on the surface of the holes 27. The highly focused interrogation beam 100 creates a large optical intensity gradient of approximately 109mW / cm3. The unrestricted surface 202 of the surface-relief photopolymer layer 200 undergoes surface relief modulation in response to variations in optical intensity on the scale of Mw / cm2 over micron scale lengths (i.e., an optical intensity gradient). approximately 10 Mw / cm3). In this way, when subjected to the high intensity gradient generated by the interrogation beam 100 focused on the surface of the holes 27, the unrestricted surface of the photopolymer layer 200 of surface relief suffers from large surface deformations 210 (see figure 3B). When the surface relief deformation 210 on the surface 202 'grows to some threshold size, it causes an aberration of the interrogation beam 100 which therefore no longer focuses on the surface of the holes 27 with sufficient sharpness to be reflected as a reflected beam 102 detectable by the photodetector 34 (see figure 2). This results in reading failure. The exposure time for the unrestricted surface 202 to form a surface deformation of the desired size to cause aberration of the interrogation beam depends on the mixture and viscosity of the polymer of the surface relief layer 200. The polymer blend and viscosity of the The photopolymer in the layer 200 can be selected so that the surface relief strains 210 of the desired size are formed immediately afterwards but not during the application of the interrogation beam 100 when reading the disk 20 for the first time. This in effect results in the disk becoming unreadable after the disk is read once. Alternatively, the polymer mixture and viscosity of the surface relief layer 200 can be selected to form the surface relief deformation of the desired size after a predetermined number of interrogation beam applications, which consequently converts to the unreadable disc after the disc has been read the predetermined number of times. Considering this, the reading procedure can be modified so as to repeatedly scan the interrogation beam on the same portion (s) of the disk surface, thereby ensuring that the surface relief polymer will be affected. In accordance with this embodiment of the invention, a method for converting the illegible optical disk 20 by an execution method includes the steps of: a) providing the optical disk 20 with a layer of surface relief photopolymer 200 which suffers from deformation of the optical disk 20; surface on an unrestricted surface in the presence of an optical intensity gradient, as can be generated by the interrogation beam 100; and b) irradiating the surface relief photopolymer layer with the interrogation beam 100 to induce at least one surface relief deformation on the unrestrained surface of the photopolymer layer. The surface relief deformation induced in this manner during the execution procedure causes an aberration in the interrogation beam, which avoids the focusing of the beam and interrogation at desired locations on the characteristics of the data structures 23 during the reading procedures Subsequent This results in a failure to read the data on the disk during a subsequent reading procedure. Figure 8 is an enlarged cross-sectional view of a portion of an optically readable medium 20 having a surface topography that is modified from a flat profile, and that can be used to detrimentally affect the tracking operation of the reading device according to the teachings of this invention. In this embodiment the flat surface topography is modified to a non-planar surface topography (not shown to scale in Figure 8) by the use of a photoresponsive polymer as described above, or by one of the evaporation techniques described. next, or by the provision of a surface layer that interacts with a substrate in the atmosphere, such as oxygen, water vapor, or carbon dioxide. In those cases it is not necessary to modify the transparency of the surface layer to the reading beam, such as by increasing its radiation absorption properties through a color change. In contrast, the varying surface topography, and its deviation from the expected flat surface layer topography, is sufficient to detrimentally affect the scanning operation of the reading device.

Referring now to FIGS. 4A and 4B, there is shown an enlarged cross-sectional view of the section A 'of the optical disk 20' according to a second embodiment of the present invention. The optical disk 20 'in the second embodiment of the invention is substantially similar to the optical disk 20 described above with reference to Figure 2, except as noted in another manner below. As seen in Figures 4A and 4B, in this second embodiment the optical disk 20 'includes a photosensitive layer 300 charged with oxygen (o2). The photosensitive layer 300 is disposed on the optical disk 20 'so that the interrogation beam 100 passes through the photosensitive layer 300 when the optical disk 20' is being scanned by the optical scanning head 30 (see Figure 2). The photosensitive layer 300 can be separated from the reflective layer 22 'of the optical disc 20' by a diffusion barrier 302. The lower surface 304 of the photosensitive layer 300 can be sealed from the environment by some means, such as waterproof polymer layer . When the optical disk 20 'is scanned with the optical scanning head 30, the interrogation beam 100 generated by the light source 32 passes through the photosensitive layer 300 and the diffusion barrier 302 and is focused on the surface of the holes 27 'in the reflecting layer 22' of the optical disc. Correspondingly, the focused interrogation beam 100 is then reflected from the reflecting aluminum surface of the holes 27 'as a reflected beam 102 detectable by the photodetector 34 in the scanning head 30 as mentioned above (see Figure 2). The irradiation of the photosensitive layer 300 with the interrogation beam 100 generates singlet oxygen (1o2) in the photosensitive layer loaded with oxygen (O2). The highly reactive singlet oxygen (1o2) generated in the photosensitive layer 300 diffuses through the diffusion barrier to the reflecting surface of the optical disc and reacts with the metal on the reflecting surface to oxidize the reflecting surface. The oxidation of the reflective surface, at least in the holes 27 'of the optical disc, degrades its reflectivity so that when the interrogation beam 100 hits the oxidized surface the reflection of the interrogation beam is decreased. The decrease in reflectivity can be interpreted as the presence of a flat region 25, and not a hole 27, resulting therefore in a reading failure, which is the desired result. More specifically, and by way of example, the photosensitive layer 300 contains one or more photosensitive compounds in combination with one or more solvents such as for example methanol, acetone, a 10% Freon / ethanol mixture, or a Freon mixture. at 1% / ethanol. The solvent provides a source of molecular oxygen (O2) internal to the photosensitive layer 300. With reference to Figure 6, and in accordance with the present invention, a combination of the photosensitizing compound (PS) plus electromagnetic radiation (ie light) that it has a wavelength of approximately 650nm active to the photosensitizer, in which the suitable photosensitizer can be indicated as PS. The photosensitizer is then combined with non-atmospheric molecular oxygen (O2) to produce singlet oxygen (1O2). In this embodiment of the invention, this reaction occurs within the photosensitizer layer 300 with the interrogation laser beam application 100, as when scanning the optical disk 20 '. Hence, in the region of the photosensitizer layer 300 through which the interrogation beam passes, the photosensitive compound becomes activated and combines with molecular oxygen (O2) provided from the solvent which is internal to the 300 layer. to produce singlet oxygen (1O2). After generation of the photosensitizer layer 300 the singlet oxygen (1O2) proceeds to diffuse through the diffusion barrier 302 to the reflecting surface of one or more of the holes 27 '. The singlet oxygen (1O2) reaches the reflecting surface and begins to chemically attack the metal after a TD delay time. The delay time TD is sufficient to allow the interrogation beam 100 to be reflected as a reflected beam 102 by the surface of the hole 27 '., and therefore allows reading of the data encoded therein before the singlet oxygen (1O2) attacks the hole surface. Accordingly, the diffusion barrier 302 can be used to delay oxidation of the reflective surface 28 'of the optical disc until the disc reading has been completed at least once. The delay time TD for the singlet oxygen (1o2) to diffuse through the diffusion barrier 302 depends on the thickness h of the diffusion barrier 302 and the diffusion capacity D of the singlet oxygen diffusion barrier ( 1 or 2). The relationship between the diffusion delay time TD, the thickness h and the diffusion capacity of the barrier 302 is generally described by the equation: r. - (D) The diffusion barrier 302 comprises an appropriate medium that it does not extinguish the singlet oxygen (1o2) and has a controlled D diffusion capacity. For example, the diffusion capacity D of the diffusion barrier 302 can vary on a scale of about 10.5 to 10.g cm2 / sec depending on the material selected for the barrier 302. Accordingly, the TD delay time can be controlled to be greater than the time required to read the encoded data in the reflective layer 22 'of the disc 20' by selecting a material with the appropriate diffusion capacity D and selecting an appropriate thickness h for the diffusion barrier 302. However, the delay time TD is restricted by the life time fH) of the singlet oxygen (1o2). The life time Ti of the singlet oxygen (1o2) is a function of the hydrophobic and paramagnetic properties of the host. The following are examples of general TT life times for singlet oxygen (1o2) for different solvents: Ti (μseg) Solvent 7 methanol 45 acetone 150 freon / ethanol (10%) 1400 freon / ethanol (1%) Therefore, the diffusion barrier 302 separating the photosensitizing layer 300 from the reflective layer 22 of the optical disk is dimensioned suitably to provide a TD delay time for singlet oxygen diffusion that is both greater than the reading time (Tile) and less than the Ti life time of the singlet oxygen (1o2) (i.e., Ti> T0 >); Construction) - Two suitable materials for the diffusion barrier 302 are polyurethane or Teflon ™, while suitable materials for the photosensitizing layer 300 include a polymer doped with phthalocyanine, such as polycarbonate or PMMA, or a polymer impurified with a derivative of porphyrin, or other high triplet yield dye. Other suitable materials could also be used, and these specifically listed materials should not be read in a limiting sense when practicing this invention. Referring now to Figures 5A and 5B, there is shown an enlarged cross-sectional view of the section A "of the optical disk 20" according to a third embodiment of this invention. The optical disk 20"in this embodiment of the invention is substantially similar to the optical described optical disc 20 described above with reference to Figure 2, except as mentioned in another manner below, as seen in Figures 5A and 5B, the optical disc 20"in accordance with this embodiment includes a substrate 400 that can be formed from a polycarbonate material disposed generally against the reflective surface 28" of the reflective layer 22"on the optical disc. Between the substrate 400 and the reflective surface 28"of the disc 20" are included regions of cavities 402A, 402B of an uncured photopolymer 402. As shown in Figure 5A, the photopolymer 402 is disposed within the holes 27" formed in the reflective layer 22"of the optical disk 20." In an uncured state, the refractive index of the photopolymer 402 is such that the interrogation beam 100 generated by the light source 32 (see FIG. 2) passes through. both of the substrate 400 and the uncured photopolymer 402, and the interrogation beam 100 is focused to the surface of the holes 27". The uncured photopolymer 402 is adapted to cure after illumination by light having a suitable wavelength, for example, about 650 nm, although the photopolymer can be adapted to cure when irradiated with light having other wavelengths. Therefore, illumination by the interrogation beam 100 of the optical scanning head 30 (e.g., laser light having a wavelength of about 650 nm) cures the photopolymer 402 after a given period (i.e., causes entanglement between the photopolymer molecules, resulting in a change in viscosity and a general solidification of the photopolymer). After the photopolymer is cured, the refractive index of the photopolymer 402 changes such that the interrogation beam 100 directed to the pits 27"and passing through the cured photopolymer 402 '(as shown in Figure 5B) no longer focused on the surface of the holes 27". That is, the curing of the photopolymer material results in aberration of the beam, and a loss of focus within the hole 27. "Therefore, in accordance with this embodiment of the invention, illuminate the uncured photopolymer 402 in the holes 27. "of the optical disk 20", as when reading the disk for the first time or during multiple steps after the initial reading, cures the photopolymer after the photopolymer 402 'is cured, such as that which is disposed in the holes 27" , it defocuses the interrogation beam 100 in such a way that it is no longer reflected as reflected lightning 102 detectable by the photodetector 34. This in turn causes a reading failure, which is the desired result. The uncured photopolymer 402 preferably has a curing time that allows a first-time reading free of impediments (ie, interrogation beam 110 is reflected by a hole 27"as reflected beam 102 which is detectable by the photodetector 34 before that the photopolymer heals) but prevents the subsequent reading of hole 27. " Suitable photocurable polymers, such as acrylic resins, include wavelength sensitized resins, such as those generally used in photolithography or in some rapid prototyping applications with, for example, argon or krypton excitation lasers. General reference can be found with respect to photopolymers in the U.S. patent. No. 5,028,109, issued July 2, 1991, entitled "Methods for manufacturing polymeric waveguides of frequency duplication having an optimally efficient periodic modulation zone and polymer waveguides manufactured therefrom".

Reference may also be made in the literature to other suitable photoresponsive polymers, such as those mentioned in the US patent. No. 4,865,942, "Photoresistible Compositions Containing a Dye-Borate Complex and Photosensitive Materials Employing Them", by Gottschalk et al. The above three embodiments of this invention render an optical disk 20, 20 ', 20"illegible, or limit its viability to perhaps no more than four hours after first reading (i.e., running) the optical disk with the scanning system Optics 1. Further, the three embodiments of the present invention accomplish this without making the optical disk 20, 20 ', 20"susceptible to becoming illegible prematurely from relevant optical conditions such as, for example, sunlight or interior lighting . Typical interior illumination in general will not adversely affect the viability of the optical disc 20, 20 ', 20"in the three preferred embodiments of the present invention, however, in the event that possible exposure to sunlight is a cause of However, a narrow band filter material (not shown) can be deposited on the lower surface 26 of the disc to prevent sunlight activation of the polymeric medium (s) of choice. is merely illustrative of the invention For example, the step of directing the interrogation beam can be carried out by directing the beam on the optical disk for a continuous period sufficient to cause the reaction in the photopolymer layer 200, 402 or photosensitizing layer 300. Alternatively, the interrogation beam can be directed on the disk in individual periods that cumulatively trigger the reaction. and interrogation can be conducted in individual periods during a single disk scan or over a multiple number of disk scans. A fourth embodiment of this invention will now be described. This fourth embodiment is intended to provide a method for interrupting an optical signal such as that used in reading a DVD or CD by evaporating a substance. This method is therefore also useful in the construction of optical discs that become illegible after a certain time. This method provides a means to generate color, which is capable of absorbing a beam of interrogation light, by evaporating a substance. By way of introduction, it is known that certain substances color or change color during changes in the solvent or environment. An example is the class of lactone dyes that are used in copying papers without carbon. The colorless lactone form of the dye may be caused to "open" to the colored cationic form of the dye by absorption into an acidic clay or other acidic substrate, reducing the pH of the lactone in solution, or changing the polarity of the solvent in the which the lactone is dissolved. The colorless lactone form and the colored cationic form of an example of lactone dye, crystal violet lactone, is shown in figure 7. It has been shown that polymers derived from phenol and formaldehyde are effective in causing the opening of a dye of lactone (see U.S. Patent No. 4,578,690), probably due to the acid nature of the phenolic component. A test was performed using poly-p- (hydroxystyrene) obtained from Hoechst-Celenese (MW = 6300) to determine if this polymer also caused the crystal violet lactone to open and color. A solution of the polymer in THF was mixed with a small amount of crystal violet lactone and this solution was placed on a glass plate and air dried. Upon drying, a dark blue spot formed. It was observed that the polymer-lactone solution remained colorless until the mixture dried, after which the intense color of the cationic form of the dye was formed. This mechanism forms the basis of this embodiment of the invention, that is, of using a mixture of solvents, a relatively volatile one and a second one that is relatively non-volatile, to prepare the polymer-lactone solution. When the solution is dried, the less volatile solvent remains during the evaporation of the more volatile solvent, and the mixture remains colorless until the less volatile solvent evaporates in a given period. Mixtures of poly-p- (hydroxystyrene) (PHS), ethanol (as the most volatile solvent), crystal violet lactone (CVL) and several less volatile solvents (LVS) were prepared. Drops of the mixtures were allowed to air dry at room temperature and the color of the remaining films was recorded to see what effect the less volatile solvent had during the generation of color.

Preparation of the solutions: PHS Ethanol CVL LVS C Color Solution # 1 500 mg 2.0 ml 20 mg 300μl NMP - Solution # 2 500 mg 2.0 ml 20 mg 300μl TEGDME + Solution # 3 500 mg 2.0 ml 20 mg 300μl BA ++ Solution # 4 500 mg 2.0 ml 20 mg 300μl THN +++. denotes that there is no color, +++ denotes intense color formation Solvent Name PE ° C Value Z NMP N-methylpyrrolidinone 202 65 • j Q TEGDME Dimethyl ether of triethylene glycol 216 60 BA Benzyl alcohol 205 75 THN Tetrahydronaphthalene 207 55 * The Z value is a measure of relative polarity. L Looss vvaalloorreess aanntteess lliissttaaddooss are estimates.

From the above experiment, NMP was chosen as the best of the less volatile solvents tested since the polymer film 15 remained colorless during the evaporation of the ethanol.

EXAMPLE 1 A solution of poly-p- (hydroxystyrene) (5 gm), ethanol 0 (10 ml), crystal violet lactone (200 mg and NMP (3.0 ml) was prepared.A few drops were applied to a glass slide and the mixture The film formed was soft and sticky to the touch but was colorless.The color formation was followed over the course of several days by the use of a spectrophotometer.

Time (hours) Optical density (607 nm) 0 0 18 0.181 85 0.242 Because the film formed in Example 1 was soft and sticky formaldehyde was added to entangle the phenolic polymer.

EXAMPLE 2 A solution of poly-p- (hydroxystyrene) (5 gm), ethanol (10 ml), crystal violet lactone (220 mg), 28% ammonia (0.5 ml as an entanglement catalyst) and NMP (3.0 ml) was prepared. . To this solution, 37% aqueous formaldehyde (3.0 ml) was added. A few drops were applied to a glass slide and the mixture was cured at about 65 ° C on a hot plate until the film was hard. This took approximately 5 minutes. The film that was formed was hard to the touch and was colorless after the cure. The color formation was followed during the course of several days by the use of a spectrophotometer.

Time (hours) Optical density (607 nm) 1 0 24 0.270 50 0.315 EXAMPLE 3 To test the color stability of the system in storage, a film was prepared as described in Example 1. The air-dried glass slide was sealed in a polyethylene zippered bag together with a drop of NMP to form a saturated environment of NMP in the bag. The slide stored in this manner showed no color formation after one week at room temperature. Upon being removed from the bag, color was started as in Examples 1 and 2. The slide was dark blue with an optical density of 0.875 to 605 nm after five days in the air at room temperature. The dissipation of light rather than absorbance can also be used to attenuate an optical signal. An evaporation method to cause increased dissipation can be achieved by mixing a polymer with a solid where there is an inequality between the refractive indexes of the two materials, and then adding a solvent so that the polymer that adjusts the refractive index of the mixture of polymer-solvent matches that of the solid. Under these conditions the mixture is not dissipating or dissipating in a deficient manner since there is a coincidence of refractive index between the polymer-solvent pair and the solid. However, the slow evaporation of the solvent causes an inequality between the remaining polymer and the solid and, consequently, the dissipation increases.

EXAMPLE 4 A solution of 1.0 gm of cellulose acetate butyrate (CAB, MW = 70,000, 13.5% acetyl, 37.5% butyryl, n = 1.46) in 20 ml of ethyl acetate was prepared and to this solution was added 1.0 gm of gel of silica (70-230 mesh, n about 1.50) and 600 μl of benzyl alcohol (n about 1.54). A drop of this mixture was placed on a glass slide and the ethyl acetate was allowed to evaporate to provide a clear film, transparent through which newspaper could be easily read. Being in the air for two days the film became quite murky and the newspaper could be read through the film only with difficulty. In accordance with the teachings of this invention, one or both of the above evaporation-based methods can be used to render an optically readable medium, such as DVD or CD, unreadable after some time. Referring by way of example to Figure 2, the upper protective layer 24 could comprise one of the blends described in Examples 1 and 2 above, which is initially colorless and transparent, but which becomes colored and becomes absorbent after sufficient has occurred solvent evaporation. The upper protective layer 24 could also comprise the CAB-ethyl acetate solution referred to in Example 4, which is initially colorless and transparent, but which becomes turbid and dissipative after sufficient evaporation has occurred. solvent. While it may be preferred to have this exposed layer as a more superior layer, it is also within the scope of the invention to apply a coating, as long as the coating is sufficiently permeable to allow the evaporation process to occur. It can be understood that this embodiment of the invention does not require the presence of atmospheric oxygen either, since evaporation could also take place in a vacuum, nor does it require the presence of a ray of light to catalyze or initiate the process, since the change Color or increase in opacity and dissipation can also occur in a dark compartment, as long as the evaporation process is not significantly impeded. Other methods for attenuating an optical signal may also be employed to practice this invention. For example, it is well known that salts of a weak acid and a weak base in which either the acid or base or both are volatile will return to the free acid and free base to be outdoors due to the volatilization of one of the components . An example of this is solid ammonium carbonate, which slowly sublimes in the open air due to the formation of the volatile components of salt, ammonia and carbon dioxide. This property can be used to generate color and therefore optical absorption in different ways. For example, the salt of a volatile amine and a non-volatile acid component (carboxylic acid, phenol, etc.) can be mixed with a lactone dye, such as crystal violet lactone, or with a pH indicator dye. The volatilization of the basic component (amine) will leave the acid component behind. The acid component can be used to catalyze the opening of the lactone dye, or cause the color change in a pH indicator. The volatilization of a gas can also be used to generate a color. For example, a polymer film moistened with water containing a pH indicator dye can be stored in an atmosphere of a gas whose water solution is acidic (eg, carbon dioxide, sulfur dioxide) or basic (ammonia, triethylamine). , etc.). Upon removal of the film from the atmosphere the volatile gas will evaporate from the film wetted with water, and the pH will change causing a color change in the pH indicator dye. This type of mechanism has been used to detect carbon dioxide and amines (see Mills, et al.Anal Chem 1992, 64, 1383, Lakowicz et al., Biotechnol.Prog. 1998, 14, 326, and US patents 5,183,763 and 5,846,836). The increase in absorbance or light dissipation (or both) can be achieved by coating a chemically reactive layer, exemplified by the various examples given above, on the surface of a disc, using methods such as spin coating, spray, Slot coating, or vacuum reservoir. The deposit with pattern can be done by a printing procedure, such as printing with silk stencil or inkjet, or with stencils for spray painting using spray or vacuum coating. Alternatively, the reactive layer can be prepared separately as an adherent plastic film, cut to size, and applied to the surface of the disc. In addition, timed read disabling can occur by increasing the dissipation from the interrogation laser beam, thus degrading the overall signal-to-radio ratio (SNR) level to an unacceptable level. This approach is less susceptible to changes in laser energy, error correction codes, or improved detector design. Also, by way of example, the vacuum deposition of thin layers of sensitive inorganic materials, such as KBr or CsF, on the surface of the disk can provide a surface haze when exposed to an atmospheric substance, such as water vapor and / or carbon dioxide, thus increasing at least one of photoabsorption, dissipation, or roughness of surface, and thus also reducing the SNR. In addition, by way of example, the evaporation of a volatile solvent from a polymer coating can lead to the precipitation of small dissipating crystals, or evaporation could lead to a phase change of a polymer or polymer mixture with light dissipation. concomitant. Also, as mentioned above, the disabling of timed reading may also occur by reducing the reflectance capacity of the reflective metal coated surface (s) of the disk.

This method is susceptible to the same factors mentioned above for the increase in absorbance. It should be mentioned that the corrosion of the hidden reflecting layer is essentially irreversible. The adhesive layer on both CD and DVD can be modified to exploit the corrosive effects of air on metals. Because an object of the present invention is to provide short life disks, the use of different materials is an option, compatible with the manufacturing capacity. The composition of the adhesive and the plastic can be adjusted to specifications to promote a corrosive reaction, once the disc packaging is removed. Also, the reflective layer itself can be made using metals more reactive than aluminum, such as potassium or calcium. This invention can be practiced by providing an optically encoded medium with two or more of the above embodiments. For example, an optical disk can be constructed to provide the characteristic of surface deformation as well as the oxidation characteristic of the aluminum layer, or the absorption induced by evaporation and / or change of dissipation in combination with the oxidation of reflecting metal, thus ensuring the effective destruction of the disc after it has been read initially. Accordingly, those skilled in the art can devise various alternatives and modifications without departing from this invention. Accordingly, the present invention is intended to include such alternatives, modifications and variations that fall within the appended claims.

Claims (41)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for rendering an optically readable medium illegible by an execution method, comprising the steps of: providing the medium with an optically activated mechanism that degrades the reflectivity of a surface where the information is encoded; expose the medium to optical radiation to read the information; and during the step of exposing, start the operation of the optically activated mechanism.

2. The method according to claim 1, further characterized in that the step of initiating comprises the steps of: generating singlet oxygen in a layer disposed in the medium; and reacting the singlet oxygen with a metal-containing layer to oxidize the surface of the metal-containing layer, thereby degrading the reflectivity of the surface.

3. The method according to claim 2, further characterized in that the step of generating includes a step of dissipating the singlet oxygen through a diffusion barrier that is disposed between the layer and the metal-containing layer.

4. A method for rendering an optically readable medium illegible by means of an execution method, comprising the steps of: providing the medium with an optically activated mechanism that causes a defocusing of the read beam, thereby degrading the reflection of the reading beam of a surface where the information is encoded; expose the medium to optical radiation to read the information; and during the step of exposing, start the operation of the optically activated mechanism.

5. The method according to claim 4, further characterized in that the step of initiating comprises the steps of: generating a gradient of optical intensity in a layer disposed in the medium; and in response to the generated gradient, deforming a surface of the layer resulting in at least one of aberration of the read beam or a degradation of a read tracking function.

6. The method according to claim 5, further characterized in that the step of providing provides the layer to comprise a polymer containing azobenzene.

7. The method according to claim 4, further characterized in that the step of initiating comprises the steps of: irradiating a region of photocurable polymer comprising the medium; and in response to radiation, photopolymerize the polymer, thereby changing a refractive index of the polymer which results in an aberration of the reading beam.

8. An optically readable medium capable of being made unreadable by an execution method, said means comprising an optically activated mechanism that responds to the light used to read information to degrade the reflectivity of a surface where the information is encoded.

9. The medium according to claim 8, further characterized in that said mechanism comprises a photosensitizing compound for reacting with oxygen molecules that are pre-charged within a layer to generate singlet oxygen in the layer, the singlet oxygen reacting with a metal-containing layer to oxidize the surface of the metal-containing layer, thus degrading the reflectivity of the surface.

10. The medium according to claim 9, further comprising a diffusion barrier disposed between said layer and said metal-containing layer.

11. An optically readable medium capable of being rendered illegible by an execution method, said means comprising an optically activated mechanism that responds to the light used to read information to defocus a reading beam, thereby degrading the reflection of the reading beam of a reading beam. surface where the information is encoded.

12. The medium according to claim 11, further characterized in that said mechanism comprises a polymer layer that responds to a gradient of optical intensity generated by said read beam to deform a surface of said layer resulting in lightning aberration of reading.

13. - The medium according to claim 12, further characterized in that said layer comprises a polymer containing azobenzene.

14. The medium according to claim 11, further characterized in that said mechanism comprises at least one region comprising a photoresponsive polymer that responds to the read beam to be light-cured, thereby changing a refractive index of the photocurable polymer resulting in aberration of the reading beam.

15. A method for rendering readable to an optically readable medium comprising the steps of: providing the medium with a layer comprising a volatile component and at least one other component; removing at least some of the volatile component, and causing an increase in at least one of photoabsorption or dissipation or surface roughness with the remaining component.

16. The method according to claim 15, further characterized in that the other component comprises a lactone dye.

17. The method according to claim 15, further characterized in that the other component comprises crystal violet lactone.

18. The method according to claim 15, further characterized in that the layer comprises poly-p- (hydroxystyrene), ethanol, crystal violet lactone and N-methylpyrrolidinone.

19. - The method according to claim 15, further characterized in that the layer comprises poly-p- (hydroxystyrene), ethanol, crystal violet lactone, ammonia, N-methylpyrrolidinone. and formaldehyde.

?

20. The method according to claim 15, t 5 further characterized in that the layer comprises cellulose acetate butyrate, ethyl acetate, silica gel and benzyl alcohol.

21. The method according to claim 15, further characterized in that the layer comprises a salt of a volatile amine, a non-volatile acid component and a lactone dye.

22. The method according to claim 15, further characterized in that the layer comprises a salt of a volatile amine, a non-volatile acid component and a pH indicator dye.

23. The method according to claim 15, further characterized in that the layer comprises a polymer film 15 moistened with water containing a pH indicator dye, further characterized in that during storage the layer is exposed to an atmosphere of a gas whose water solution is acidic or basic, and wherein upon removal from storage a volatile gas evaporates from the film wetted with water, and the pH changes causing a color change in the pH indicator dye.

24. The method according to claim 15, further comprising a preliminary step of constructing the layer as a separate component layer, and then a step of applying the separated component layer to a surface of the optically readable medium.

25. A method for rendering readable an optically readable medium, comprising the steps of: providing the medium with a layer comprising a sensitive inorganic material; exposing the layer to an atmosphere containing a substance comprising at least one of water vapor or carbon dioxide; and reacting the inorganic material with the substance to cause an increase in at least one of photoabsorption or dissipation or surface roughness.

26. The method according to claim 25, further characterized in that the layer comprises KBr.

27. The method according to claim 25, further characterized in that the layer comprises CsF.

28. An optically readable medium comprising a pattern structure for encoding information that can be read by applying light, said optically readable medium further comprising a layer comprising a volatile component and at least one other component in which to eliminate at least some of the The volatile component causes an increase in at least one of photoabsorption or dissipation or surface roughness with the remaining component, thereby making it legible to at least a portion of the encoded information.

29. - The medium according to claim 28, further characterized in that the other component comprises a lactone dye. ^ 30.- The medium according to claim 28,

5 further characterized in that the other component comprises a crystal violet lactone.

31. The medium according to claim 28, further characterized in that the layer comprises poly-p- (hydroxystyrene), ethanol, crystal violet lactone and N-methylpyrrolidinone.

The medium according to claim 28, further characterized in that the layer comprises poly-p- (hydroxystyrene), ethanol, crystal violet lactone, ammonia, N-methylpyrrolidinone and formaldehyde.

33. The medium according to claim 28, further characterized in that the layer comprises cellulose acetate butyrate,

15 ethyl acetate, silica gel, and benzyl alcohol. «*

34. The medium according to claim 28, further characterized in that the layer comprises a salt of a volatile amine, a non-volatile acid component and a lactone dye.

35. The medium according to claim 28, further characterized in that the layer comprises a salt of a volatile amine, a non-volatile acid component and a pH indicator dye. 36.- The medium according to claim 28, further characterized in that the layer comprises a layer of polymer moistened with water containing a dye indicator of pH, where during storage the layer is exposed to an atmosphere of a gas whose solution of water is acidic or basic, and where upon removal from storage a volatile gas evaporates from the film moistened with

• 5 water, and the pH changes causing a color change in the pH indicator dye.

The medium according to claim 28, further characterized in that said layer is applied by a coating or printing process or as a separate component layer 10 applied by adhesive.

38.- An optically readable medium comprising a pattern structure for coding information that can be read by applying light, said optically readable medium further comprising a layer comprising a sensitive inorganic material wherein the exposure of said layer to an atmosphere containing a substance causes a reaction between the inorganic material and the substance to cause an increase in at least one of photoabsorption or dissipation or surface roughness, thus making it readable to at least a portion of the encoded information.

39. The medium according to claim 38, further characterized in that the layer comprises KBr.

40.- The medium according to claim 38, further characterized in that the layer comprises CsF.

41. - A method to make it readable to an optically readable medium, comprising the steps of: providing the medium with a surface layer having a flat surface topography; and subsequent to during a first reading of the optically readable medium, modifying at least a portion of the flat surface topography to a non-planar surface topography by using at least one of a photoresponsive polymer, a removal of a substance from the layer from surface to atmosphere, or by interaction with a substance in the atmosphere without significantly modifying a transparency of the surface layer to a reading beam, wherein a deviation of the non-planar surface topography of the topography from The flat surface layer is sufficient to harmfully affect at least one scanning operation of a reading device that generates the read beam.