WO2010107784A1 - Procédé de contrôle d'activation d'une photopolymérisation pour le stockage de données holographiques à l'aide d'au moins deux longueurs d'onde - Google Patents

Procédé de contrôle d'activation d'une photopolymérisation pour le stockage de données holographiques à l'aide d'au moins deux longueurs d'onde Download PDF

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WO2010107784A1
WO2010107784A1 PCT/US2010/027466 US2010027466W WO2010107784A1 WO 2010107784 A1 WO2010107784 A1 WO 2010107784A1 US 2010027466 W US2010027466 W US 2010027466W WO 2010107784 A1 WO2010107784 A1 WO 2010107784A1
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wavelength
optionally substituted
group
media
recording
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PCT/US2010/027466
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English (en)
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Eric S. Kolb
David A. Waldman
Richard A. Minns
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Stx Aprilis, Inc.
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Publication of WO2010107784A1 publication Critical patent/WO2010107784A1/fr

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only
    • G11B7/245—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing a polymeric component
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/0005—Production of optical devices or components in so far as characterised by the lithographic processes or materials used therefor
    • G03F7/001—Phase modulating patterns, e.g. refractive index patterns
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/004—Photosensitive materials
    • G03F7/038—Macromolecular compounds which are rendered insoluble or differentially wettable
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/20—Exposure; Apparatus therefor
    • G03F7/2022—Multi-step exposure, e.g. hybrid; backside exposure; blanket exposure, e.g. for image reversal; edge exposure, e.g. for edge bead removal; corrective exposure
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/02—Details of features involved during the holographic process; Replication of holograms without interference recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0065—Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/083—Disposition or mounting of heads or light sources relatively to record carriers relative to record carriers storing information in the form of optical interference patterns, e.g. holograms
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/02—Details of features involved during the holographic process; Replication of holograms without interference recording
    • G03H2001/026—Recording materials or recording processes
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/02—Details of features involved during the holographic process; Replication of holograms without interference recording
    • G03H2001/026—Recording materials or recording processes
    • G03H2001/0264—Organic recording material
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2260/00—Recording materials or recording processes
    • G03H2260/12—Photopolymer

Definitions

  • holographic data storage provides the promise for fast access times , fast data transfer rates, and higher data density for optical storage.
  • information is recorded as an ensemble of interference fringe patterns formed by the intersection of two coherent energy sources in the volume of the recording material.
  • coherent light beams from lasers are utilized to perform the addressing, namely writing and reading of the data to and from the storage media by directing these beams at a specific region on the surface of the media.
  • Interference fringes are then formed within a holographic recording media (HRM) including a homogeneous mixture of monomer or oligomer and a binder and a polymerization initiator.
  • HRM holographic recording media
  • this initiation followed by polymerization, occurs in the light areas of the interference fringe pattern.
  • monomer or oligomer diffuses into the light areas of the fringe structure to be incorporated into the growing polymer chains.
  • Polymerization induced chemical segregation in the case of a diffusible binder, drives the binder into the dark regions of the fringe structure. Since the monomer or oligomer and the binder have differing index of refraction an index modulation is achieved during the exposure process, thereby forming the hologram.
  • the recording media is made sensitive to actinic radiation of a desired energy level (wavelength) by the incorporation of a photo initiator.
  • the photo initiator may absorb light energy directly or may be sensitized to a desired wavelength or energy of irradiation by incorporation of a sensitizing dye.
  • the normal polymerization procedure is to irradiate the photopolymerizable material with photons having energy that initiates the polymerization process.
  • the reaction sequence associated with this process is complex.
  • the sensitizing dye compound is first exited by a photon of proper energy, and then the excited dye transfers energy to the initiator, photo acid generator, (PAG), for example, to provide an activated initiator species, or the excited state dye reacts with the initiator via a oxidation-reduction process to form an initiative species.
  • the initiative species, or activated initiator then combines with or actives a monomer, which begins a chain reaction with additional monomers to result in polymerization.
  • the sensitizer dyes that are typically used are linear absorbers at the exposure wavelengths for recordation. These sensitizer dyes work by converting light energy into chemical initiative species at some quantum efficiency associated with the molecular make-up of the dye molecule and its chemical surroundings.
  • the use of said dye in conjunction with, by example, a PAG leads to holographic media with high recording sensitivity as well as other favorable characteristics, such as bleaching.
  • the utilization of a linear absorber yields a holographic or photo-polymerizable medium with a linear response to the exposure energy of actinic radiation.
  • the initiation of polymerization, the strength of the hologram formed and the amount of monomer or oligomer polymerized after a particular photo-initiated event is proportional to the amount of actinic radiation or exposure fluence the media has been received in a location or storage volume.
  • the process of recording a grouping of volume holograms in the same volume element is referred to co- locational multiplexing.
  • the dynamic range in a photopolymer medium is proportional to the amount of active monomer and or oligomer available for polymerization and the magnitude of the difference in the index of refraction between the monomer and the binder that chemically segregate during the recording process.
  • hologram recording can commence in a grouping of new locations until all the dynamic range in the media is fully consumed.
  • each storage location is arranged in a closest-packed geometry to optimally use the media's dynamic range and thus maximize the storage density.
  • the recordation of holograms only takes place in the beam overlap region in the hologram recording material (i.e. in the volume of the interference pattern of the recording beams). Outside the region of the interference pattern, where the reference and signal beam impinge on, or in, the recording material but do not overlap, photopolymerization is initiated at a rate, or amount, associated with the photon flux and the quantum efficiency of initiation.
  • This unintended polymerization consumes photoinitiator as well as monomers/oligomers, thus wasting the dynamic range in the volume element surrounding a particular storage location.
  • This unintended polymerization has a significant impact on the overall storage density achievable in a holographic media and is exacerbated as the thickness of the recording material increases.
  • One proposed solution to this problem is to include an inhibitor in the recording medium.
  • the inhibitor prevents premature polymerization and keeps the media in an inactive state by consuming or quenching initiating species as they are formed, either by reacting with the photoinitiator or by reacting/quenching growing polymer chain ends, thereby limiting or preventing polymerization and preventing formation of holograms.
  • the inhibitor needs to be removed or otherwise chemically reacted or depleted. After the inhibitor is depleted in a region then the initiator can then react with monomer(s) to effect polymerization and record holograms. Once the threshold exposure is achieved, depleting an inhibitor in the storage location, the hologram recording process can initiate.
  • One approach to achieve high storage density is to use a non-linear absorber as the photosensitizer in the photopolymerizable medium.
  • a two-photon process, or multi-photon process is used to create a localized region for polymerization.
  • the polymerization region is localized due to the non-linear absorption properties of the two-photon dye, where the absorption probability depends quadratically on light intensity.
  • a two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution.
  • the present invention relates to a polymerizable media in which a sensitizer is produced in situ as well as to the methods of use of such a polymerizable media.
  • a polymerizable media including at least one monomer or oligomer which undergoes polymerization to form a polymer; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer, initiates polymerization of the at least one monomer or oligomer when said sensitizer is exposed to actinic radiation of the second wavelength.
  • a method of polymerizing a polymerizable media includes at least one monomer or oligomer which undergoes polymerization to form a polymer; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer, initiates polymerization of the at least one monomer or oligomer when said sensitizer is exposed to actinic radiation of the second wavelength.
  • the method includes (a) exposing a first location in the polymerizable media to actinic radiation of the first wavelength, thereby forming the sensitizer from the compound; and (b) exposing the first location in the polymerizable media to actinic radiation of the second wavelength, thereby initiating polymerization of the at least one monomer or oligomer.
  • a method of recording a hologram in a HRM includes at least one monomer or oligomer which undergoes polymerization; a binder; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer initiates polymerization of the at least one monomer or oligomer, when said sensitizer is exposed to actinic radiation of the second wavelength.
  • the method includes (a) exposing a first storage location in the HRM to a beam of actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing actinic radiation of a second wavelength; and (b) directing a reference beam of coherent light of the second wavelength and an object beam of coherent light of the second wavelength at the first storage location, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, initiating polymerization of the at least one monomer or oligomer in the volume of the said interference pattern and thereby recording the interference pattern as a hologram within said first storage location.
  • HRM which includes at least one monomer or oligomer which undergoes polymerization; a binder; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer initiates polymerization of the at least one monomer or oligomer, when said sensitizer is exposed to actinic radiation of the second wavelength.
  • the method includes (a) exposing a first storage location in the HRM to actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing electromagnetic radiation of a second wavelength, said first storage location being located in a portion of the depth of the HRM; and (b) directing a reference beam of the second wavelength and an object beam of the second wavelength at the first storage location, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, and initiating polymerization of the at least one monomer or oligomer in the volume of the interference pattern in the first storage location and thereby recording the interference pattern as a hologram within said first storage location.
  • a portion of the depth of the HRM means a fraction of the thickness of the HRM, usually corresponding to Rayleigh length(s).
  • the fraction can be any number between 0 and 1, e.g. 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the thickness.
  • the reference or signal beam can optionally be created by reflection of the signal or reference beam, respectively.
  • a method of recording a hologram, in a HRM includes at least one monomer or oligomer which undergoes polymerization; a binder; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer initiates polymerization of the at least one monomer or oligomer, when said sensitizer is exposed to actinic radiation of the second wavelength.
  • the method includes (a) exposing a first storage location in the HRM to a beam of actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing electromagnetic radiation of a second wavelength; and (b) directing a reference beam of coherent light of the second wavelength and an object beam of coherent light of the second wavelength at the first storage location in the HRM, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, initiating polymerization of the at least one monomer or oligomer and recording the interference pattern therefrom as a hologram within said first storage location.
  • the beam of actinic radiation of the first wavelength, and the reference and object beams is each independently generated, such as by a tunable light source.
  • the sensitizer is formed in the volume of the exposure of the first storage location in the HRM, therefore the region of overlap between the reference beam and object beam of the second wavelength that occurs in the volume comprising the sensitizer formed by the exposure of the first storage location in the HRM to the first wavelength corresponds to the volume in the HRM where the interference pattern is recorded as a hologram.
  • an optical article in another aspect, includes one, or two or more substrates; and a HRM thereon or therebetween.
  • the HRM includes at least one monomer or oligomer which undergoes polymerization; a compound, which absorbs actinic radiation of a first wavelength and forms a sensitizer which absorbs actinic radiation of a second wavelength; and an initiator, which, in combination with the sensitizer, initiates polymerization of the at least one monomer or oligomer when said sensitizer is exposed to actinic radiation of the second wavelength.
  • a media for holographic recording that exhibits a controlled threshold for a recording event. Consequently, multiple recordings (e.g., multiplexed holograms) can be made in a given volume of the polymerizable media without loss of dynamic range due to depletion of photoreactive media components or undesirable light absorption on the sensitizer dye molecules.
  • the polymerizable media and the disclosed methods provide for substantial increase in the storage density, as illustrated in FIG. 5.
  • the polymerizable media and disclosed methods allow for the recording of one or more holograms at a sensitized active location in a HRM while substantially no preconsumption of dynamic range of the HRM (e.g. due to spillover of the holographic recording beams) occurs at unsensitized inactive locations in the HRM.
  • This feature is an improvement over certain prior sensitizable HRM, in which preconsumption of dynamic range was reduced but not substantially eliminated at inactive locations in the HRM.
  • FIG. 1 is a schematic diagram showing an exemplary optical architecture for recording Fourier transform volume holograms, according to various embodiments.
  • FIG. 2 is a schematic diagram showing a portion of the HRM at the area of impact of the object and reference beams, according to various embodiments.
  • FIG. 3(A) is a schematic representation of one embodiment of the optical geometry of reference beam and the object beam, according to various embodiments.
  • FIG. 3(B) illustrates a detail of FIG. 3(A) at the area where the reference and object beams are incident onto the HRM, according to various embodiments.
  • FIG. 4 is a schematic representation a selected storage location in a
  • HRM in cross section view being illuminating with actinic radiation at a first wavelength 1' that activates the storage location in the HRM for recording holograms, according to various embodiments.
  • FIG. 5 is a plot the storage density in bits/ ⁇ m 2 as a function of thickness of the recording material in ⁇ m, according to various embodiments.
  • FIG. 6 is a plot showing diffraction efficiency, ⁇ , of multiplexed holograms as a function of recording exposure energy E, according to various embodiments.
  • FIGs. 7A and 7B are 1 HNMR spectra for compound S7-closed.
  • FIG. 8 is a 1 HNMR spectra for compound S8a.
  • FIG. 9 is a graph of the Photo Differential Scanning Calorimetry
  • PDSC 5,5"-Dimethyl-2,2':5',2"-terthiophene
  • FIG. 10 is a comparative graph of the PDSC results for open and closed compound S7, according to the examples.
  • FIG. 11 is a graph showing the growth in cumulative grating strength versus the cumulative recording fluence in mJ/cm for the nine co-locationally multiplexed planar angle volume holograms recorded in the material at the second wavelength ( ⁇ 2 ) immediately after the in situ activation was carried out at the first wavelength (X 1 ) and after a wait time of 17 hours after the same activation step before recording at the second wavelength ( ⁇ 2 ), according to the examples.
  • FIG. 12 is a graph showing the recording sensitivity versus the cumulative recording fluence in mJ/cm 2 for the nine co-locationally multiplexed planar angle volume holograms recorded in the material at the second wavelength ( ⁇ 2 ) immediately after the in situ activation was carried out at the first wavelength (X 1 ) and after a wait time of 17 hours after the same activation step before recording at the second wavelength ( ⁇ 2 ), according to the examples.
  • actinic radiation refers to any electromagnetic radiation capable of initiating photochemical reactions. It includes microwave, IR, VIS and UV wavebands.
  • conjugation refers to a set of contiguous and covalently bonded atoms where each atom posses a p-orbital and the molecular arrangement results in a derealization of electrons across adjacent parallel aligned or substantially parallel aligned p-orbitals.
  • delocalized refers to orbital character where the electrons are distributed or shared along a contiguous sequence of atoms.
  • alkoxy, alkylammonium, and the like is preferably a straight chain or branched saturated aliphatic group with 1 to about 12 carbon atoms, e.g., methyl, ethyl, n- propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl or octyl, or a saturated cycloaliphatic group with 3 to about 12 carbon atoms.
  • cycloalkyl means saturated cyclic hydrocarbons, i.e. compounds where all ring atoms are carbons.
  • examples of cycloalkyl include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl.
  • haloalkyl includes an alkyl substituted with one or more F, Cl, Br, or I, wherein alkyl is defined above.
  • alkoxy means an "alkyl-O-" group, wherein alkyl is defined above.
  • alkoxy group include methoxy or ethoxy or propoxy or butoxy groups and may be branched.
  • an "alkenyl group”, alone or as a part of a larger moiety is preferably a straight chain or branched aliphatic group having one or more double bonds with 2 to about 12 carbon atoms, e.g., ethenyl, 1-propenyl, 1-butenyl, 2-butenyl, 2-methyl-l-propenyl, pentenyl, hexenyl, heptenyl or octenyl, or a cycloaliphatic group having one or more double bonds with 3 to about 12 carbon atoms.
  • an alkynyl group is preferably a straight chain or branched aliphatic group having one or more triple bonds with 2 to about 12 carbon atoms, e.g., ethynyl, 1-propynyl, 1-butynyl, 3- methyl-1-butynyl, 3, 3 -dimethyl- 1-butynyl, pentynyl, hexynyl, heptynyl or octynyl, or a cycloaliphatic group having one or more triple bonds with 3 to about 12 carbon atoms.
  • an "aryl”, alone or as part of a larger moiety is a carbocyclic aromatic group, preferably including 6-22 carbon atoms.
  • Suitable aryl groups for the present invention are those which 1) do not react directly with light in the absence of an initiator to initiate or induce polymerization of any type, and 2) do not interfere with polymerization. Examples include, but are not limited to, carbocyclic groups such as phenyl, naphthyl, biphenyl, anthracenyl, and phenanthryl.
  • heteroaryl refers to aromatic groups containing one or more heteroatoms (O, S, or N).
  • a heteroaryl group can be monocyclic or polycyclic, e.g. a monocyclic heteroaryl ring fused to one or more carbocyclic aromatic groups or other monocyclic heteroaryl groups.
  • the heteroaryl groups of this invention can also include ring systems substituted with one or more oxo moieties.
  • heteroaryl groups include, but are not limited to, pyridinyl, pyridazinyl, imidazolyl, pyrimidinyl, pyrazolyl, triazolyl, pyrazinyl, quinolyl, isoquinolyl, tetrazolyl, furyl, thienyl, isoxazolyl, thiazolyl, oxazolyl, isothiazolyl, pyrrolyl, quinolinyl, isoquinolinyl, indolyl, benzimidazolyl, benzofuranyl, cinnolinyl, indazolyl, indolizinyl, phthalazinyl, pyridazinyl, triazinyl, isoindolyl, purinyl, oxadiazolyl, thiazolyl, thiadiazolyl, furazanyl, benzofurazanyl, benzothiophenyl,
  • heteroaryl groups may be C-attached or N-attached
  • a group derived from pyrrole may be pyrrol- 1- yl (N-attached) or pyrrol-3-yl (C-attached).
  • Suitable substituents on alkyl, alkoxy, alkenyl, alkynyl, aryl, and heteroaryl groups are those which 1) do not react directly with light in the absence of an initiator to initiate or induce polymerization of any type and 2) do not interfere with polymerization.
  • suitable substituents include, but are not limited to Cl -C 12 alkyl, C6-C14 aryl, -OH, halogen (-Br, -Cl, -I and -F), -O(R'), -O-CO-(R'), - COOH, -N(R') 2 , -COO(R'), -S(R') and -Si(R' 3 ).
  • Each R' is -H or independently a substituted or unsubstituted aliphatic group or a substituted or unsubstituted aryl group.
  • R' is an unsubstituted alkyl group or an unsubstituted aryl group.
  • R' is a C1-C12 alkyl, C1-C12 halogenated alkyl, C3-C10 cycloalkyl; in other embodiments, more preferably R' is methyl, ethyl, 2-ethylhexyl, cyclohexyl, benzyl or a phenyl group.
  • R' is a phenyl substituted with one or more substituent groups such as Cl -C 12 alkyl, Cl -C 12 halogenated alkyl, C3-C10 cycloalkyl, halogen, phenyl or benzyl, or C1-C12 alkoxy, optionally substituted with C1-C12 alkyl or C1-C6 haloalkyl or C3-C10 cycloalkyl.
  • substituent groups such as Cl -C 12 alkyl, Cl -C 12 halogenated alkyl, C3-C10 cycloalkyl, halogen, phenyl or benzyl, or C1-C12 alkoxy, optionally substituted with C1-C12 alkyl or C1-C6 haloalkyl or C3-C10 cycloalkyl.
  • the substituents on phenyl are methyl, ethyl, 2-ethylhexyl, Cl -C 12 fluorinated or perfluorinated alkyl, cyclohexyl, benzyl, phenyl, 2-ethylhexyloxy, - OCH 3 , chloro, or trifluoromethyl.
  • alkyl, alkoxy, alkenyl, alkynyl, aryl, and heteroaryl groups can optionally be substituted with one or more halogen, hydroxyl, Cl -C 12 alkyl, C2-C12 alkenyl or C2-C12 alkynyl group, Cl -C 12 alkoxy, or Cl -C 12 haloalkyl.
  • substituents for a substitutable carbon atom in alkyl, alkoxy, alkenyl, alkynyl, aryl, and heteroaryl groups include but are not limited to -OH, halogen (-F, -Cl, -Br, and -I), -R, -OR, -CH 2 R, -CH 2 OR, -CH 2 CH 2 OR. Each R is independently an alkyl group.
  • a C6-C14 aryl is a phenyl, indenyl, naphthyl, azulenyl, heptalenyl, biphenyl, indacenyl, acenaphthylenyl, fluorenyl, phenalenyl, phenanthrenyl, anthracenyl, cyclopentacyclooctenyl or benzocyclooctenyl.
  • a 5-14-membered heteroaryl group is a pyridyl
  • a C6-C14 aryl is a phenyl, naphthalene, anthracene, lH-phenalene, tetracene, or pentacene.
  • a C6-C14 aryl is an indenyl, azulenyl, heptalenyl, biphenyl, indacenyl, acenaphthylenyl, fluorenyl, phenalenyl, phenanthrenyl, cyclopentacyclooctenyl or benzocyclooctenyl.
  • a C6-C14 aryl is a phenyl, naphthalene, anthracene, tetracene, or pentacene.
  • a 5-14-membered heteroaryl group is a pyridyl, furanyl, thienyl, pyrrolyl, imidazolyl, quinolinyl, pyrazolyl, indolyl, purinyl, or benzothienyl.
  • a 5-14-membered heteroaryl group is a 1-oxo- pyridyl, benzo[l,3]dioxolyl, benzo[l,4]dioxinyl, isoxazolyl, isothiazolyl, isoquinolinyl, benzofuryl, imidazopyridyl, pyrrolo[2,3]pyrimidinyl, pyrazolo[3,4]pyrimidinyl, or imidazo[l,2-a]pyridyl.
  • a 5-14- membered heteroaryl group is a pyridyl, furanyl, thienyl, pyrrolyl, imidazolyl, pyrazolyl, indolyl, and benzothienyl.
  • any of the above C6-C14 aryl and/or 5-14- membered heteroaryl are optionally substituted.
  • the substituents are selected from one or more of C1-C12 alkyl, C6-C14 aryl, -OH, halogen, -O(R'), -O-CO-(R'), - COOH, -N(R') 2 , -COO(R'), -S(R') and -Si(R' 3 ).
  • the substituents are one or more of C1-C12 alkyl, -OH, halogen (preferably F, Cl, Br, or I), -O(R'), -O-CO- (R'), -N(R') 2 , -COO(R'), and -Si(R' 3 ). More preferably, the substituents are one or more of C1-C12 alkyl, -OH, -F, -O(C1-C12 alkyl), amine, -N(R') 2 , and -Si(R' 3 ).
  • R' can be any of the above C6-C14 aryl or 5-14-membered heteroaryl groups, or a C1-C12 alkyl, C1-C12 halogenated alkyl, C3-C10 cycloalkyl.
  • R' is a C1-C12 alkyl, C1-C12 halogenated alkyl, C3-C10 cycloalkyl; more preferably, R' is -H, methyl, ethyl, 2-ethylhexyl, cyclohexyl, benzyl or a phenyl group.
  • a "binder” refers to a compound or composition used in the polymerizable media which is chosen such that it does not inhibit polymerization of the monomers used, such that it is miscible with the monomers used as well as the polymerized or copolymerized structure, and such that its refractive index is significantly different from that of the polymerized monomer or oligomer.
  • the refractive index of the binder differs from the refractive index of the polymerized monomer by at least 0.04. In other embodiments, the refractive index of the binder differs from the refractive index of the polymerized monomer by at least 0.09.
  • the refractive index of the binder differs from the refractive index of the polymerized monomer 0.04 to 0.20.
  • a binder is inert to the polymerization processes of the one or more polymerizable monomer(s).
  • the binder is diffusible.
  • diffusable refers to a material that may migrate or reorganize in a polymerizable media, as the polymerization of the media progresses.
  • Diffusible binders can, by way of example, segregate from the polymerizing monomer(s) or oligomer(s) during holographic recording via diffusion-type motion of the binder component.
  • binders for use in HRM are polysiloxanes, due in part to availability of a wide variety of polysiloxanes and the well documented properties of these oligomers and polymers.
  • the physical, optical, and chemical properties of the polysiloxane binder can all be adjusted for optimum performance in the recording medium inclusive of, for example, dynamic range, recording sensitivity, image fidelity, level of light scattering, and data lifetime.
  • the efficiency of holograms produced by the present process in the present medium is markedly dependent upon the particular binder employed.
  • binders include poly(methyl phenyl siloxanes) and oligomers thereof, 1,3,5- trimethyl-l,l,3,5,5-pentaphenyltrisiloxane and other pentaphenyltrimethyl siloxanes, or cyclic siloxanes that may be optionally substituted with Cl -C 12 alkyl or optionally substituted C3-C12 cycloalkyl or an optionally substituted aryl or an optionally substituted heteroaryl. Examples are sold by Dow Corning Corporation under the trade name Dow Corning 710, Dow Corning 705, and oligio (poly)phenylethers sold as Convalex Oils have been found to give efficient holograms.
  • More preferable binders comprise a star of a multi-armed (at least 3 arms) siloxane core, wherein the terminus of each arm is a high refractive index moiety (see for example Structural Formula (I) in PCT publication WO 2007/047840 A3.
  • the refractive index of the terminus of each arm should be at least 1.545, more preferably 1.565, still more preferably 1.585.
  • multiarmed siloxane core terminated with high refractive index moieties refers to a composition of matter having the refractive index of at least 1.550, preferably at least 1.600.
  • refractive index of any one moiety attached as the terminus of an arm to the siloxane core should preferably be at least about 1.545, more preferably at least 1.565, still more preferably at least 1.585.
  • Other binders can comprise a cyclic methyl-siloxane core with pendent aromatic moieties, as shown in Structural Formula (II) in WO 2007/047840 A3, wherein n is the number of methylsiloxane units in the cyclic structure.
  • the cyclic siloxane core comprises at least 3 substituted methylsiloxane units.
  • the polymerizable media includes a compound that undergoes a molecular rearrangement reaction upon exposure to actinic radiation of the first wavelength to form the sensitizer which absorbs actinic radiation of the second wavelength.
  • a molecular rearrangement reaction upon exposure to actinic radiation of the first wavelength to form the sensitizer which absorbs actinic radiation of the second wavelength.
  • An example of such a rearrangement is a 6 ⁇ electrocyclic cyclization upon exposure to actinic radiation of the first wavelength.
  • the compound that undergoes a molecular rearrangement is a spiropyran, spiro-oxazine, fulgide (dialkylidenesuccinic anhydride), triarylmethane, naphthopyran, diarylethene or diheteroarylethene.
  • the compound is a diarylethene or a diheteroarylethene, where the aryl or heteroaryl moiety is a substituted or unsubstituted phenyl, a substituted or unsubstituted naphthyl, a substituted or unsubstituted thiophene, a substituted or unsubstituted benzathiophene, a substituted or unsubstituted pyrrole, and a substituted or unsubstituted indole.
  • the ethene moiety of the diarylethene and diheteroarylethene is optionally substituted and/or is a part of an optionally substituted cycloalkene, an optionally substituted anhydride, or optionally substituted maleimide.
  • the cycloalkene moiety is a C4-C6, optionally perfluorinated, cycloalkene.
  • alkyl, alkenyl, aryl and heteroaryl groups and suitable substituents are as described above for the corresponding groups.
  • the compound that undergoes a molecular rearrangement is represented by the following structural formula:
  • ring C is an optionally fluorinated or perfluorinated C3-C7 cycloalkenyl and ring C is an optionally fluorinated or perfluorinated C3-C7 cycloalkane;
  • X 1 is a linker group that provides for conjugation between Ar 1 and the thienyl group with which X 1 is connected;
  • X 2 is absent or is a linker group that provides for conjugation between Ar 2 and the thienyl group with which X 2 is connected;
  • Ar 1 is an optionally substituted C6-C22 aryl or an optionally 5-14-membered heteroaryl;
  • Ar 2 is independently an Ar 1 , wherein the optical absorbance characteristics for the Ar 1 or Ar 2 moiety can be for a specific wavelength or range of wavelengths of actinic radiation.
  • -X 2 -Ar 2 is an electron donating group or an electron withdrawing group.
  • R 3 and R 4 are each independently selected form a Cl-Cl 2 alkyl group, a Cl-Cl 2 alkenyl group, or a Cl-C 12 alkoxy group.
  • Preferred alkyl, alkenyl, aryl and heteroaryl groups and suitable substituents are as defined above for the corresponding groups.
  • linker refers to a moiety which: 1) does not react under conditions which induce or initiate polymerization; 2) does not interfere with polymerization; 3) does not interfere with chemical segregation of the binder from a polymer formed during polymerization; 4) and provides for conjugation between the groups linked together.
  • linking groups include, but are not limited to, an alkenyl group, an alkynyl group, a carbonyl group, a grouping including a carbonyl, a sequence of alternating single and double bonds (e.g.
  • X 1 and X 2 are the same. In other embodiments, X 1 and X 2 are not the same.
  • Ar 1 for each occasion is independently optionally substituted with a group represented by R y , where R y is an optionally substituted Cl -C 12 alkyl, an optionally substituted C2-C12 alkenyl, an optionally substituted C2-C12 alkynyl, an optionally substituted C3-C12 cycloalkyl, an optionally substituted C3-C12 cycloalkenyl, an optionally substituted C6-C14 aryl, or an optionally substituted 5-14-membered heteroaryl or is an electron- donating group selected from Cl -C 12 alkoxy, Cl -C 14 dialkylamine, and a C6-C14 diarylamine, or is an electron-withdrawing group selected from -NO 2 , -CF 3 , C1-C4 trialkylammonium, -C(O)OR', -CN, -SO 3 R', and a halogen,
  • each linker group is independently an ethynyl group or an ethenyl group; Ar 1 is an optionally substituted C6-C22 aryl; and Ar 2 is an optionally substituted C6-C22 aryl.
  • Ar 1 is substituted or unsubstituted phenyl, naphthyl, or anthracenyl; and Ar 2 is substituted or unsubstituted phenyl, naphthyl, or anthracenyl.
  • VI, Ar 1 and Ar 2 have the values as described in the previous paragraph and are independently unsubstituted or substituted with an optionally substituted Cl -C 12 alkyl, optionally substituted C2-C12 alkenyl, optionally substituted C2-C12 alkynyl, optionally substituted C3-C12 cycloalkyl, optionally substituted C3-C12 cycloalkenyl, optionally substituted C6-C14 aryl, an optionally substituted 5-14- membered heteroaryl, an optionally substituted Cl -C 12 alkoxy, Cl -C 14 dialkylamine, a C6-C14 diarylamine, -NO 2 , -CF 3 , C1-C4 trialkylammonium, -C(O)OR', -CN, -SO 3 R', or a halogen, and further wherein R' is -H or a Cl-Cl 2 alkyl.
  • Ar 1 and Ar 2 are independently unsubstituted or substituted with -Si(R 5 ) 3 ; C1-C12 alkyl group, optionally substituted with -Si(R 5 ) 3 , a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, C1-C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; or a 5-14-membered heteroaryl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen,
  • Ar 1 and Ar 2 are independently unsubstituted or substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.
  • each linker group is an ethynyl group; and Ar 1 and Ar 2 are anthracen-9-yl or 6- methoxynaphthalen-2-yl. In other embodiments, each linker group is thienyl.
  • X 1 is phenyl or 5-6 membered heteroaryl and X 2 is absent, wherein the group represented by X 1 is optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl- C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.
  • X 2 is absent and X 1 is thienyl optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkyl, Cl -C 12 haloalkoxy or cyano.
  • Ar 1 is optionally substituted phenyl or optionally substituted thienyl; and Ar 2 is optionally substituted phenyl.
  • Ar 1 is optionally substituted thienyl.
  • X 1 and for the embodiments described in the previous paragraph is phenyl or 5-6 membered heteroaryl and X 2 is absent
  • Ar 1 and Ar 2 are independently unsubstituted or substituted with an optionally substituted Cl -C 12 alkyl, optionally substituted C2-C12 alkenyl, optionally substituted C2-C12 alkynyl, optionally substituted C3-C12 cycloalkyl, optionally substituted C3-C12 cycloalkenyl, optionally substituted C6-C14 aryl, an optionally substituted 5-14-membered heteroaryl, an optionally substituted C1-C12 alkoxy, Cl- C14 dialkylamine, a C6-C14 diarylamine, -NO 2 , -CF3, C1-C4 trialkylammonium, -C(O)OR', -CN, -SO 3 R', or a halogen, and further wherein R'
  • Ar 1 and Ar 2 are independently unsubstituted or substituted with - Si(Rs) 3 ; C1-C12 alkyl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, C1-C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, or C1-C12 alkylamine; a 5-14-membered heteroaryl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine,
  • Ar 1 and Ar 2 are independently unsubstituted or substituted with halogen, Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkyl, Cl- C 12 haloalkoxy or cyano.
  • Ar 1 is optionally substituted with Cl -C 12 alkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl and Cl -C 12 haloalkyl and the group represented by Ar 2 is optionally substituted with halogen, Cl -C 12 alkyl, Cl- C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkyl, Cl -C 12 haloalkoxy or cyano.
  • -X 2 -Ar 2 is an electron withdrawing group.
  • -X 2 -Ar 2 is halogen, Cl -C 12 alkyl or
  • X 1 is phenyl or 5-6 membered heteroaryl and wherein the group represented by X 1 is optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl- C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.
  • X 1 is thienyl optionally substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano.
  • Ar 1 is preferably optionally substituted phenyl or thienyl.
  • -X 2 -Ar 2 is as described in the previous sentences and Ar 1 is optionally substituted thienyl.
  • Ar 1 is unsubstituted or substituted with an optionally substituted Cl -C 12 alkyl, optionally substituted C2-C12 alkenyl, optionally substituted C2-C12 alkynyl, optionally substituted C3-C12 cycloalkyl, optionally substituted C3-C12 cycloalkenyl, optionally substituted C6-C14 aryl, an optionally substituted 5-14-membered heteroaryl, an optionally substituted C1-C12 alkoxy, Cl- C14 dialkylamine, a C6-C14 diarylamine, -NO 2 , -CF 3 , C1-C4 trialkylammonium, -C(O)OR', -CN, -SO 3 R', or a halogen, and further wherein R' is -H or a Cl -C 12 alkyl.
  • the group represented by Ar 1 is unsubstituted or substituted with -Si(Rs) 3 ; C1-C12 alkyl group, optionally substituted with -Si(R 5 ) 3 , a Cl -C 12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, C1-C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; or a 5-14-membered heteroaryl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen,
  • Ar 1 is unsubstituted or substituted with halogen, Cl -C 12 alkyl, Cl -C 12 haloalkyl, Cl -C 12 alkenyl, Cl -C 12 haloalkenyl, Cl -C 12 alkoxy, Cl -C 12 haloalkoxy or cyano. More preferably, Ar 1 is optionally substituted with C1-C12 alkyl, C1-C12 alkenyl, Cl -C 12 haloalkenyl and Cl -C 12 haloalkyl and the group represented.
  • Ar 1 is thienyl optionally substituted with F, Cl, Br, I, CN, Cl -C 12 alkyl, or haloalkyl.
  • Ar 1 is a hexylthienyl group, a phenyl group, a methoxyphenyl group, a naphthyl group, an anthracenyl group, a phenylanthracenyl group, a methoxyanthracenyl group, or methylthienyl group; and Ar 2 is a hexylthienyl group, a phenyl group, a methoxyphenyl group, a naphthyl group, an anthracenyl group, a phenylanthracenyl group, a methoxyanthracenyl group, methylthienyl group, a triflu
  • ring C is preferably a perfluorocyclopentene and ring C is a perfluorocyclopentane.
  • Another embodiment of the invention is a compound of Formula V or
  • sensitizers described and depicted below are intended to be instructive and are by no means limiting as to the scope of the present invention:
  • the Sensitizer dye can be asymmetric wherein the substituents directly on the ethene moiety are not the same, e.g.,
  • Ar 1 , Ar 2 , or Ar 3 can have optical absorbance characteristics at a specific wavelength or grouping of wavelengths of actinic radiation.
  • Ar 1 , Ar 2 , or Ar 3 for each occasion is independently optionally substituted with a group represented by an optionally substituted Cl -C 12 alkyl, an optionally substituted C2-C12 alkenyl, an optionally substituted C2-C12 alkynyl, an optionally substituted C3-C12 cycloalkyl, an optionally substituted C3-C12 cycloalkenyl, an optionally substituted C6-C14 aryl, or an optionally substituted 5-14-membered heteroaryl or is an electron-donating group selected from Cl -C 12 alkoxy, Cl -C 14 dialkylamine, or a C6-C14 diarylamine.
  • the optional substituent for each occurrence is independently selected from -Si(Rs) 3 ; C1-C12 alkyl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; Cl -C 12 alkenyl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, or Cl- C12 alkylamine; C6-C14 aryl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, or Cl -C 12 alkylamine; a 5-14-membered heteroaryl group, optionally substituted with -Si(Rs) 3 , a C1-C12 alkoxy, a halogen, an amine, or C1
  • X is a linker group that provides for conjugation between Ar 3 and the thienyl group with which X 1 is connected.
  • the formed sensitizer is a linear absorbing dye.
  • the formed sensitizer is a non-linear-absorbing dye.
  • the formed sensitizer is a 2-photon absorbing dye.
  • the polymerizable media includes an initiator.
  • the initiator can initiate any type of a polymerization reaction.
  • the initiator is a photoacid generator (PAG), wherein the PAG produces acid in combination with the sensitizer.
  • PAG photoacid generator
  • the PAG is a sulfonium, sulfoxonium, iodonium, diazonium, or phosphonium salt.
  • At least one monomer or oligomer included into the polymerizable media undergoes cationic polymerization.
  • the monomer or oligomer which is capable of undergoing polymerization contains one or more epoxide, oxetane, cyclic ether, 1-alkenyl ether, unsaturated hydrocarbon, lactone, cyclic ester, lactam, cyclic carbonate, cyclic acetal, aldehyde, cyclic sulfide, cyclosiloxane, cyclotriphosphazene, or polyol functional groups, or a combination thereof.
  • the epoxide monomer is a siloxane or siloxysilane including two or more cyclohexene oxide groups, or a polyfunctional siloxane including three or more cyclohexene oxide groups.
  • the monomer is an epoxide monomer that includes one or more cyclohexene oxide groups.
  • suitable siloxane monomers can be found in aforementioned U.S. Patent Nos. 6,784,300 and 7,070,886 and PCT Publication WO 02/19040.
  • the polymerizable media includes an initiator that is a free radical generator, and wherein the free radical generator produces free radicals in combination with the sensitizer.
  • the polymerizable media includes at least one monomer or oligomer undergoes free radical polymerization.
  • the produced free radicals initiate free radical polymerization reactions.
  • the initiator is a photoacid generator (PAG), wherein the PAG produces acid in combination with the sensitizer.
  • the PAG is a sulfonium, sulfoxonium, iodonium, diazonium, or phosphonium salt.
  • An example of a sensitizer that can be formed from a compound in such a polymerizable media is diphenylanthracene.
  • a method of polymerizing a polymerizable media includes (a) exposing a first location in the polymerizable media to actinic radiation of the first wavelength, thereby forming a sensitizer from the compound in a volume in the first location; and (b) exposing the first location in the polymerizable media to actinic radiation of the second wavelength, thereby initiating polymerization of the at least one monomer or oligomer in volume in the said first location.
  • a method of recording a hologram includes steps (a) exposing a first storage location in the HRM to a beam actinic radiation of the first wavelength, thereby forming a sensitizer from the compound, said sensitizer absorbing actinic radiation of a second wavelength; and (b) directing a reference beam of coherent light of the second wavelength and an object beam of coherent light of the second wavelength at the first storage location, thereby forming an interference pattern at the first storage location between the object beam and the reference beam, initiating polymerization of the at least one monomer or oligomer and thereby recording the interference pattern as a hologram within said first storage location.
  • the sensitizer is formed from the compound in the volume of the exposure of the first storage location in the HRM, therefore the region of overlap between the reference beam and object beam of the second wavelength that occurs in the said volume comprising the sensitizer formed by the exposure of the first storage location in the HRM to the first wavelength is the volume in the HRM where the interference pattern is recorded as a hologram.
  • a hologram can be a binary data page hologram.
  • the data page hologram can be recorded with an object beam that is amplitude modulated or phase modulated and a reference beam that, by way of example, is a collimated or spherical wavefront and can optionally be phase coded or phase modulated.
  • the hologram can be a micrograting recorded in a portion of a volume of the first storage location in the HRM such as a portion of the depth of the volume.
  • the micrograting can be recorded in a portion of the volume in the thickness direction of the HRM at the first storage location or in portion of the volume in the lateral direction at the first storage location, or combinations thereof.
  • One or more microgratings can be recorded in a portion of the volume of the first storage location by repeating step (b) at the first storage location, thereby recording multiplexed microgratings that overlap at least in part in the said portion of the volume of the first storage location.
  • the multiplexed microgratings can be recorded with two or more different wavelengths or two or more different phases.
  • steps (a) and (b) can be repeated, and for each repetition of step (a), step (b) is repeated one or more times. Steps (a) and (b) can occur substantially at the same time.
  • steps (a) and (b) are performed at a second location in the polymerizable media.
  • the second location can be abutting or at least partially overlapping the first location in one or more directions. Alternatively, the second location is neither abutting or overlapping the first location.
  • the beam of actinic radiation of the first wavelength, the reference beam or the object beam are produced by a source of actinic radiation that is a continuous emitting source or a pulsed source.
  • a source of actinic radiation include a frequency doubled diode pumped solid state laser (DPSS) or diode laser, and further, wherein the diode laser optionally includes an external cavity that is optionally temperature controlled.
  • the beam of actinic radiation of the first wavelength, the reference beam, or the object beam is each independently generated by a tunable light source such as tunable laser.
  • the beam of actinic radiation of the first wavelength is a light emitting diode (LED).
  • the beam of actinic radiation of the first wavelength is a collimated or a substantially collimated beam.
  • the beam of actinic radiation of the first wavelength, the reference beam or the object beam can each independently have a Gaussian intensity distribution at the first storage location.
  • the beam of actinic radiation of the first wavelength, the reference beam or the object beam can each independently have a truncated Gaussian intensity distribution at the first location in the HRM, wherein the minimum diameter of the truncated Gaussian intensity distribution is less than or equal to the diameter of said beam, measured at the 1/e intensity point.
  • exposing the first location to actinic radiation of the first wavelength, the reference beam or the object beam exposes a volume element of the HRM having a cross-sectional area that changes as a function of depth through the HRM.
  • the amount of formed sensitizer can be controlled by the intensity of the actinic radiation of a first wavelength or by the duration of the exposure of the compound to the actinic radiation of a first wavelength or combinations thereof.
  • the actinic radiation of a first wavelength can be used as a source of light for generating a servo signal from the media.
  • the method of polymerizing the media and the method of recording a hologram can further include a step (c) of reading the recorded hologram after recording the hologram at the first storage location, wherein the reading step confirms the recording of the hologram at the first storage location (i.e. direct read after write).
  • Step (c) can further include reading the recorded micrograting hologram after recording the micrograting hologram at the first storage location, wherein the reading step confirms the recording of the micrograting hologram at the first storage location.
  • the method of polymerizing the media and the method of recording a hologram can further include performing steps (a) and (b) at a second storage location in the HRM before steps (a) and (b) or step (b) are repeated at the first storage location in the HRM for recording multiplexed holograms at the first storage location. Steps (a) and (b) are repeated at the first storage location for recording multiplexed holograms at the first storage location, after performing steps (a) and (b) at the second storage location in the HRM.
  • This embodiment can be useful for further homogenizing recording sensitivity, such as during recording along a track on a disk or card, where multiple passes along the track can occur during recording so as to record using steps (a) and (b) at each of the storage locations along the track before repeating step (a) or step (b) at each of the said locations along the track.
  • the multiplexed holograms are multiplexed with at least one multiplexing method selected from planar angle multiplexing, shift-multiplexing including co-linear shift multiplexing, phase-multiplexing, phase encoded multiplexing, azimuthally multiplexing, out-of-plane tilt-multiplexing, and polytopic spatial multiplexing.
  • a media for holographic recording where multiple recordings are taking place in a simultaneous or sequential manner, or during interrupted recording sessions, to have a photoactive media that exhibits a true and controlled threshold for a recording event.
  • This is desirable for a number of reasons, for example, to simplify the recording schedule, to improve image fidelity, to improve efficiency of polymerizing monomer or oligomer for recording holograms, to improve the handling quality and possibly improve pre-recorded shelf-life.
  • initiation systems that can be activated in-situ in a specific location while the surrounding location(s) are left in an inactive state are provided.
  • the photosensitizer, the dye-like compound that imparts photosensitivity at a desired wavelength can be activated or switched from a non-reactive state to a reactive state using an external stimuli such as light, heat or a combination of both.
  • an external stimuli such as light, heat or a combination of both.
  • the dye compound can be used as an actinic light sensitizer for initiation of a photopolymerization process, where such processes could be used for micro lithography or hologram recording.
  • the media would be prepared and conditioned so as to be nonreactive to a 1 st wavelength ⁇ ⁇ , the wavelength of data recording or the desired wavelength for photo-activity.
  • Recording data would follow the steps of (1) activating a region to be recorded by action of light of a second wavelength ⁇ 2 , or by the action of heat or a combination of both, (2) followed by data recording at the desired wavelength, ⁇ ⁇ and (3); subsequently moving to a new recording location, say an abutting region or an overlapping region that is at least partially overlapping, where the process could be repeated.
  • the abutting regions are desirably inactive to the recording wavelength and thus abutting regions are not impacted by recording in neighboring areas.
  • the photosensitizer can be switched from a non- reactive state to a reactive state by a molecular reorganization such as exhibited, by way of example, in photochromic compounds.
  • a molecular reorganization may be a cis-trans isomerization.
  • the re-organization is a cycloreversion process initiated by an external stimuli such as light, heat or a combination of both.
  • the dye compound can be used as a actinic light sensitizer for initiation of a photo-polymerization process, where such processes could be for hologram recording.
  • An initiator may also be introduced into a formulation for photopolymerization and holographic recording including monomers, oligomers, binders and the like, and said initiator can be introduced in a form that makes the media substantially nonreactive to a particular and desirable wavelength of light.
  • the initiator can be converted directly or indirectly to a new species either through action of light or heat.
  • the initiator of the present invention is a photochromic compound that can be introduced into a formulation in an inactive state and that said initiator in the inactive state can be converted via a molecular reorganization to an active state by the action of light or heat.
  • photochromic compounds include but are not limited to:
  • Spiropyrans Spiropyrans, spiro-oxazines, fulgides, triarylmethanes, quinones, naphthopyrans and diarylethenes.
  • Diarylethenes are represented by stilbene, azoarene, diaryleperfluorocycloalkenes (butane, pentene, hexene), diarylmaleic anhydrides and diarylmaleimides and other such compound that undergo a reversible transformation, as indicated in the reaction scheme below, from a colorless to a colored form.
  • a dye/sensitizer is coupled to a photochromic compound or switch, wherein the dye is attached via a linking group defined above.
  • the formulation after the initiator is converted into the active state, the formulation will be reactive when exposed to actinic radiation of a desirable wavelength and that photopolymerization can occur.
  • the initiator is a photo-sensitizer that interacts with a photoacid generator, photobase generator or photoradical generator to provide an initiating species when the initiator is in the active form.
  • the heat process can be initiated via a direct method such via radiant heating.
  • the heat process can be initiated via an indirect methods by incorporation of an IR of NIR sensitive dye or a colloidal metal particle and use of an IR source or a visible light source, such as laser diode.
  • the heat step may be done via secondary process where a laser source such as an IR or near IR laser can be used to heat a location in the storage medium thereby causing a heat activated dye forming reaction.
  • the media can be made susceptible to IR or Near IR irradiance by incorporating an IR dye or colloidal metal particles to absorb said IR irradiance.
  • the IR dye can be attached to a nano-particle.
  • the precursor dye compound can be attached to a nanoparticle and that both the precursor and the IR dye can be attached to the same nanoparticle to facilitate the efficiency of dye activation.
  • Methods of reducing extinction coefficient or changing concentration of the compounds for photoinitiation can improve uniformity of developed refractive index modulation during recording as a function of depth into the recording material, however, photopolymerization is still initiated at the wavelength(s) used for recording the holograms and the extent of polymerization is directly dependent upon the magnitude of the irradiance, typically in units of mJ/cm , of the exposure used for recording. Consequently, photoinitiation of polymerization reactions occurs wherever light is incident in the volume of the material during recording, such as where the Reference beam and Object beam must overlap for formation of the interference pattern needed to record a hologram as well as where light incident from the Reference and Object beams does not overlap.
  • the Reference beam is incident at oblique angles with respect to the optical axis of the Object beam, or if the said volume of overlap has varying cross-sectional area as a function of depth through the recording material, both of which can occur during recording of volume holograms and at least one such condition generally occurs for recording of volume holograms, then an excess of the volume at or near a selected storage location(s) is exposed to light that causes photoinitiation and thus occurrence of undesirable polymerization reactions.
  • the effects of the said excess volume being exposed during a recording event is further compounded by the need to achieve as high a multiplexing number as possible for each storage location so as to achieve a high value for areal storage density, and thus a grouping of exposures are made in substantially the same storage location wherein each said exposure initiates polymerization reactions undesirably in the said excess volume.
  • NA numerical aperture
  • Nyquist aperture 1.2 '2 *2 ⁇ f/ ⁇
  • ⁇ wavelength of recording light
  • ⁇ focal length of imaging lens
  • ⁇ pitch of the pixels of the encoding device such as a spatial light modulator (SLM), or the Rayleigh length for recording of microgratings
  • SLM spatial light modulator
  • the degree of differentiation for cross-sectional area as a function of depth through the recording material also increases with NA.
  • the area of the Object beam at the Fourier plane in the recording material is Ny 2 , but, by way of example, if the Fourier plane is at the center of the recording material than the area of the Object beam is larger at or near the top and bottom surfaces of the material.
  • the Reference beam depicted as (10), by way of example, is incident upon the storage location in recording material (8) at an oblique angle with respect to the optical axis (25) of the Object beam (20), and the Reference beam (10) is incremented by an amount ⁇ t for the case of planar-angle multiplexing over an aggregate range of incident angles ⁇ , such as up to a largest incident Reference beam angle (9), wherein the magnitude of ⁇ t for the ith recorded hologram in a storage location is related inversely to the thickness of the recording material for a given optical geometry and wavelength.
  • Reference beam (10) of FIG. 1 needs to be oversized in its lateral dimension at front face of the substrate of media (5) by an amount x to compensate for it propagating at an oblique angle through thickness T g of the front substrate (e.g.
  • d is the lateral dimension of the Object beam (20) and d' is the corresponding oversize amount at the front and back surfaces of recording material (8) that is needed to provide for overlap of the interaction volume of the Reference beam (10) and Object beam (20) throughout the thickness (T p h) of the recording material (8).
  • the said oversize amount is an excess lateral dimension that results in an excess volume being undesirably exposed.
  • the lateral dimension of the Object beam (20) is depicted as being uniform throughout the thickness of the media (5), for purposes of simplification, whereas for Fourier transform holograms the lateral dimension is often a minimum in the center and is larger at or near the front and back surfaces of media (5), as shown in FIG. 3(a) and FIG 3(b), so as to maximize storage density.
  • An adjustable blocking of a portion of the Reference beam can optionally be used to reduce the amount of scattered light originating from excess volume in the substrates that may propagate in the forward direction from the substrates of media (5) into recording material (8), wherein the dimension or size of the adjustable portion can be changed as a function of the incident angle of Reference beam (10).
  • 0R e f Int is the maximum internal angle for the Reference beam (10) in recording material (8) such as for a grouping of planar-angle multiplexing recordings in a selected storage location in the material (8).
  • FIG. 3(a) is a schematic representation of one embodiment of the optical geometry of reference beam 10 and object beam 20, wherein object beam 20 is relayed by optical element 2 to HRM 8 and reference beam 10 is incident onto HRM 8 at oblique angles of incidence.
  • FIG. 3(b) illustrates a detail of FIG. 3 (a) at the area of impact of the beams 10 and 20 onto HRM 8.
  • Oe-3 for minimum acceptable signal-to-noise of the reconstructed multiplexed data page holograms for this exemplification
  • the cumulative grating strength of the recording material in an isolated storage location is set for a dynamic range of 5 per 200 ⁇ m thickness of the recording material for this exemplification and is attainable in thinner materials by use of dual multiplexing methods such as, by of example, combination of planar-angle and out-of-plane angle multiplexing.
  • the maximum internal cone angle of FT intensity distribution for the Object beam, ⁇ can thus be defined as
  • the lateral dimension of the recording Reference beam, W" must therefore be set to
  • the excess lateral dimension of the exposure area at the storage location increases monotonically with the thickness of the recording material, T ph , and, further, the dependence of areal storage density of multiplexed recording is diminished from the linear scaling of dynamic range of the recording material with material thickness, T ph , that could otherwise be exhibited if no excess lateral dimension occurred for the exposure area during recording.
  • FIG. 4 shows illumination of a selected storage location in a holographic recording medium, in cross section view, by actinic radiation at a first wavelength, ⁇ ' that activates the said medium for the step of recording holograms.
  • the lateral dimension of the exposure with actinic radiation at a first wavelength is shown as the dimension W corresponding to the minimum dimension of the object beam during recording in the volume of the selected storage location.
  • the said lateral dimension of the exposure with actinic radiation at a first wavelength can be smaller or larger than W.
  • the lateral dimension can change its size through the thickness of the recording material at the selected storage location, such as due to converging or diverging wavefronts for said illumination, and, further, can have a shape that is not symmetric in the lateral dimensions.
  • the exposure with actinic radiation at a first wavelength can have an intensity distribution that is a Gaussian intensity distribution in the volume of the selected storage location for activating the location to recording.
  • the intensity distribution of the exposure with actinic radiation at a first wavelength can be a truncated Gaussian intensity distribution such that the intensity distribution has a lateral dimension that is less than or equal to the diameter of a Gaussian beam, di /e 2, measured at the 1/e 2 intensity point of the intensity distribution, wherein d is defined to be the diameter of the beam waist for a Gaussian intensity distribution.
  • the lateral dimension of the exposure with actinic radiation at a first wavelength defines the lateral dimension that is activated for the overlap of the recording object and reference beams.
  • the light source providing for said illumination means can, by way of example, be a CW or pulsed or otherwise modulated laser such as a diode pumped solid state laser, or diode laser, or can be a continuous emitting or modulated light emitting diode, or a lamp or other suitable light source, or combinations thereof, and can optionally be tunable in wavelength.
  • a CW or pulsed or otherwise modulated laser such as a diode pumped solid state laser, or diode laser
  • the illumination means for recording includes an optical system including a means for illuminating at least one selected location that has been activated for carrying out photopolymerization in the said location of the recording material, wherein the optical system providing for said illumination means for recording can comprise one or more optical elements that, by way of example, can be one or more lens, or mirrors, or waveplates, or beamsplitters or polarizers, or combinations thereof as needed for illuminating the said activated selected location with at least one wavelength for the purpose of recording at least one hologram, and the light source for the recording illumination means can be the same light source as for the illumination means to provide for the threshold or activation event or can be another suitable light source that, by way of example, can be a CW or pulsed or otherwise modulated laser such as a diode pumped solid state laser, or diode laser, optionally with temperature controlled external cavity, or can be a continuous emitting or modulated light emitting diode, or a lamp or other suitable light source, or combinations thereof, and can optionally be
  • FIG. 5 The effect of the excess lateral dimensions of the Object beam and of the Reference beam can be represented as shown in FIG. 5 as a function of increased thickness of the recording material for the parameters defined above.
  • the plot shows the theoretical relation between achievable storage density in bits/ ⁇ m and thickness of the recording material in ⁇ m when the requirements for excess lateral dimensions of the Reference beam and Object beam are not considered for achieving optimal overlap throughout the depth of the material.
  • 5 further shows the diminution in achievable storage density for the case of planar-angle multiplexing, when all of the dynamic range in a storage location cannot be consumed due to the limitations imposed by Bragg selectivity criteria as a function of thickness of the recording material, and additionally for the case of dual multiplexing when all of the dynamic range can be consumed in a storage location for a value that linearly scales as 5/200 ⁇ m thickness.
  • the achievable cumulative grating strength for the ensemble of multiplexed volume holograms recorded in a selected storage location is undesirably substantially reduced from what otherwise could be achieved if excess lateral dimensions were not required for proper overlap of the Reference and Object beams in the interaction volume of the storage location, and, further, the scaling of achievable storage density versus thickness of the recording material, T ph , is clearly not linearly increasing with the thickness, T p h, as otherwise expected from the theoretical relation between cumulative grating strength, storage density and thickness.
  • a method for photoinitiation of polymerization during recording volume holograms is to threshold or activate the holographic recording events by (i) providing for a recording material that is otherwise not sensitive or is inactive to the recording and/or reading wavelength(s) until the threshold or activation event has occurred, and (ii) further providing a means to create and/or control the amount of the photoinitiator or sensitizer compound(s) that is formed in the recording material in one or more selected storage locations in an induced activation event prior to and/or at the time of recording, for the expressed purpose of activating photoinitiation processes that can be used to initiate polymerization reactions during the recording of holograms, or otherwise activate polymerization reactions for recording of holograms, particularly in the case of thicker materials, wherein the said created amount (i.e.
  • concentration is at least the amount of the photoinitiator or sensitizer compound required for any specific holographic recording exposure or desired grouping of exposures that record at least one hologram(s) at the recording wavelength, such as in a grouping of multiplexed recording events.
  • chemistry of recording can still occur), such as reading from storage locations previously recorded along an z 4 track when recording can still be carried out elsewhere on the z th track or in another track or location that may be abutting or at least partially overlapping or otherwise affected by light incident from scattered light, fluorescence, stray light, oversized area of illumination compared to the area of the stored information, or other sources of incident light that arise during recording at and/or reading from said locations in the z th track, does not alter the ability to record or write information later in locations along the z -th track or proximal tracks of said media.
  • the reference beam covers an area at or near the front of the recording material that is displaced laterally from the area it exits or impinges upon at the opposing surface of the said recording material.
  • the Reference beam is preferably oversized relative to the Object beam such that the cross-section area of its illumination overlaps the cross-section area of illumination of the Object beam at all depths throughout the said recording material in which the recording is to occur.
  • the Object beam is incident upon the recording material at angles more oblique than the Reference beam then the Object beam is preferably oversized relative to the Reference beam.
  • the oversized Reference or Object beam causes photosensitization and thus initiation of polymerization reactions to take place in a cross-section area that is larger than the cross-section area corresponding to the holographically stored information at substantially all depths in the selected storage location in which the recording is to occur.
  • the undesired polymerization reactions in the volume of the selected storage location wastes chemistry that can otherwise be utilized for formation of holograms at one or more storage locations, so as to maximize areal density in said locations, and, consequently, the undesired reactions can reduce recording sensitivity and achievable dynamic range, and thus substantially limit the attainable storage density. This undesirable effect is exacerbated as thickness of the recording material is increased.
  • a method and apparatus are provided for photoinitiating polymerization or otherwise initiating polymerization for holographic recording in one or more selected locations in a recording media such that the initiation of polymerization reactions for recording holograms in said locations exhibits a threshold to the recording wavelength(s) provided by the optical system of the apparatus.
  • the one or more selected locations in the recording media are substantially insensitive or inactive to the wavelength of recording laser light provided by the optical system of the apparatus unless and until the threshold event for sensitizing the medium to the recording wavelength(s) has firstly occurred in the one or more selected locations.
  • the term "insensitive” or “inactive” shall mean a chemical state of the medium, such as a photochemical state of the medium, or conformational state of molecular compounds in the medium, or other chemical or physical chemical structural state of components of the medium, in which photoinitiation of polymerization of the polymerizable compounds in one or more selected locations in the recording material for recording holograms is substantially insensitive or inactive to light at the recording wavelength(s) that is incident said locations unless the threshold or activation event that results in activating the medium so that polymerization events can be initiated using the wavelength(s) of the recording laser light to record holograms has firstly occurred.
  • the threshold or activation event of the present invention and the recording events for recording holograms may occur sequentially or simultaneously in a selected storage location in the recording medium, or may occur sequentially or simultaneously in a grouping of selected storage locations in the recording medium.
  • the required said threshold event for creating an active chemical state in at least one selected location in the recording medium for sensitizing the selected volume in the recording medium to record holograms at the recording wavelength(s) provides the means to prevent or otherwise substantially mitigate the effects of the excess lateral dimension of the Reference beam and, optionally the Object beam, from diminishing the areal information density that is achievable if such said excess dimension did not occur and, further, prevent or substantially diminish undesirably consuming monomer intended for polymerization reactions that are optimally for recording holograms.
  • the threshold event for sensitizing the medium to the recording wavelength(s) can preferably occur by use of light and/or heat for in- situ creation of the desired population of the active compound(s) in the volume of a selected storage location, said created active compound to be subsequently utilized for the process of photoinitiation of polymerization or other means of initiation of polymerization at the recording wavelength in the said volume of said storage location so as to provide a means for recording holograms at the recording wavelength.
  • the in-situ created active compound resulting from the said threshold or activation event can act as a linearly absorbing dye compound for photoinitiating polymerization reactions for the purpose of recording holograms, such as, for example, by the methods of free radical, cationic, anionic or step polymerization reactions.
  • the in-situ created active compound resulting from said threshold event can act directly, such as, for example, by formation of a compound capable of acting as an acid or base or radical initiator, to initiate polymerization reactions for recording holograms in the selected storage location.
  • the population or concentration of the in-situ created active compound is both controllable by the threshold or activation event and, additionally, relates to the subsequent recording sensitivity in the selected storage location.
  • the selected storage location for inducing the threshold event for in situ creation of the active compound may be a location at any position in the recording media, that, by way of example, can be any position about the area of the media such as any position along a tangential, radial or helical direction, or row or column direction, and, further, the induced threshold event at said selected location may occur throughout the thickness of the recording material at the selected location, or at any thickness location or position within the recording material that includes a thickness that is less than the thickness of the recording material such as may be desired for recording information in one or more layers in the recording material.
  • the population or concentration of the in situ created compound can be substantially uniform throughout the thickness of the recording material or, alternatively, can be non-uniform such as, for example, to compensate for the transmission function of the recording light that propagates through the recording material and may be used during recording of one or more holograms at the selected storage location.
  • the size of the selected location in the recording material for inducing the threshold or activation event for in situ creation of the active compound may be a size that is equal to or substantially similar to the desired area of the selected storage location for recording one or more holograms, or the size may be an area that is larger or smaller than the desired area of the selected storage location for recording one or more holograms. If the threshold or activation event occurs by use of light incident upon one or more selected locations of the recording medium, then the wavelength of light for inducing the threshold or activation event is preferably different from the wavelength used for recording or reading the holograms, so that illumination of a selected storage location that is not firstly prepared or activated by the said threshold event results in substantially no polymerization reactions for recording holograms.
  • the storage system can further provide for direct read after write capability to verify recording of holograms with suitable diffraction efficiency and/or signal-to-noise characteristics, such as may be desired for purposes of error checking, alignment tracking or checking, in-situ evaluation of recording sensitivity and/or remaining dynamic range in a storage location, adjustment of exposure times or intensity of exposure, and the like.
  • the design of apertures for defining lateral dimensions of recording area at a storage location and/or reading from one or more storage locations can be substantially simplified.
  • Said apertures of the apparatus and method of the present invention may be different sizes for the illumination wavelength(s) used for the threshold or activation event by comparison to the illumination wavelength(s) used for recording or reading holograms.
  • the media of the apparatus and method of the present invention can be encased or otherwise protected in a cassette or other suitable holder that is primarily used to protect it from dust, dirt, particulate, scratching, etc., rather than from exposure to light having the recording or reading wavelength.
  • the recorded holograms by way of the induced said threshold event can exhibit improved uniformity of refractive index modulation achieved during recording as a function of depth into the volume hologram, particularly for thick recording materials on the order of 500 microns or thicker.
  • the optical density in the volume of the storage location can be optionally tuned or controlled in relation to the created population of the active species for photoinitiation for each recording event or a grouping of recording events specifically for the recording sensitivity that is needed or otherwise desired for said recording event(s).
  • the in-situ tuning of the optical density for recording events at one or more selected locations can take into account the declining population of monomer in the volume of the selected location(s), as well as other consumable compounds that may be part of the photoinitiation or other initiation process for the polymerization reactions, so as to provide for more uniform recording sensitivity throughout the manifold of the grouping of multiplexed recordings in the selected storage location.
  • the threshold event for creation of the population of the active species for photoinitiation of polymerization reactions for holographic recording events can be optionally carried out from the reverse direction of the propagation direction of the Reference and/or Object beams for recording holograms, so as to further compensate for absorbance effects on intensity of transmitted light through the thickness of the recording material during recording events.
  • recording sessions can be interrupted along a recording track, whether along tangential or radial directions or other suitable directions over the surface area of the media or the thickness direction in the recording material, and may even be interrupted within a selected storage location for advantageous recording of smaller amounts information then by comparison to restrictions imposed by single recording sessions for an entire media or for recording sessions carried out along one or more tracks in tangential or radial directions or along row or column directions, or carried out in one or more layers or in one or more directions within one or more layers.
  • the method and apparatus it is provided to threshold or activate volume holographic recording by providing for a recording material that is otherwise not sensitive to the recording and/or reading wavelength until the threshold or activation event has occurred, and to control the amount formed of a sensitizer compound or other compound, in one or more locations in the recording media, to the amount of an active compound that is needed for any specific multiplexed holographic exposure or grouping of exposures for recording holograms at the recording wavelength, wherein the holograms can be recorded throughout the thickness such as for the case of binary data page holograms or, alternatively, in an increment of thickness such as corresponding to the double Rayleigh length that relates to the thickness of micro-localized gratings.
  • heat and/or a first wavelength can be used to activate or pre-sensitize the recording media in the volume of a selected storage location that is to be used subsequently for one or more recording events, and the media can, preferably, be substantially insensitive or inactive to the recording wavelength until the threshold or activation event occurs.
  • the threshold or activation event can comprise application of heat and/or illumination of the recording media at the one or more desired selected storage locations, such as with a diode laser, light emitting diode, diode pumped solid state laser, flash lamp and the like, that outputs light at a first wavelength or grouping of first wavelengths hereinafter referred to as first wavelength.
  • the apparatus and method of the present invention can provide illumination with a diode laser, light emitting diode, diode pumped solid state laser or flash lamp at a first wavelength and can, by way of example, use one or more lens elements or one or more reflective optical elements, or combinations thereof, or other suitable optical components including, for example, beamsplitters, waveplates, gratings, dichroic films, optical filters, polarizers and the like to provide said illumination.
  • Said first wavelength can be longer or shorter than the wavelength used for hologram recording or reading, such that substantially no absorbance exists at the recording or reading wavelength at the selected location for active initiation of polymerization reactions prior to the induced threshold or activation event, or optionally only nominal low absorbance exists near the recording or reading wavelength prior to the threshold event, wherein the said nominal low absorbance can only result in slow photoinitation induced polymerization or other initiation induced polymerization reactions, or substantially incomplete polymerization reactions at the recording or reading wavelength.
  • the threshold or activation event can comprise illumination at a combination of 1 st wavelengths, such as in a stepwise fashion, or, alternatively, simultaneously such as emitted, by way of example, from a light emitting diode or flash lamp or from two or more light sources that output light of different wavelengths, wherein the 1 st wavelengths are longer or shorter than the recording or reading wavelength such that substantially no absorbance exists at the recording or reading wavelength, prior to the threshold or activation event, that can activate initiation of polymerization, or only nominal low absorbance exists near the recording or reading wavelength prior to the threshold event such that substantially no photoinitation induced polymerization, or relatively slow photoinitation induced or other initiation induced polymerization reactions occurs at the recording or reading wavelength, or substantially incomplete polymerization reactions occur at the recording or reading wavelength.
  • the shape of the exposed area at a selected storage location when illuminated by the 1 st wavelength to induce the threshold or activation event for formation of the desired photoinitiation or initiator compound can be a circle or square or rectangle or diamond or oval or other suitable shape.
  • the area at the Fourier plane for recording data page holograms in the recording material (8) will be W as it will be a square of dimension W on all sides corresponding the Nyquist aperture.
  • the exposed area at the top or bottom surface of the recording material (8) can similarly be a square of area W , and the illumination at the said 1 st wavelength can propagate through the depth of the recording material (8) so as to have a uniform cross section area of W at all depths within the material, as shown in FIG. 4. This can be achieved, for example, by use of collimated illumination for said 1 st wavelength.
  • the exposed area can be within the material at a certain depth position in the material, and can extend through the depth dimension by an amount that exceeds the lateral dimension of the exposed area but is less than the total thickness of the recording material, such as would be the case for recording micro-localized gratings wherein the lateral dimension of the exposed area for a typical micrograting is on the order of about 200 nm to 1000 nm.
  • the direction of said illumination at said 1 st wavelength for the threshold or activation event can be the same direction as the propagation of the Object beam and/or Reference beam used during recording of the volume holograms in the storage location.
  • the direction of the said illumination at said 1 st wavelength for the threshold or activation event can be in the opposing direction to the propagation direction of the Object beam and/or Reference beams so as to provide for formation of a concentration profile of the photo initiation compound created by the threshold event, said profile being in the reverse direction of the transmission function occurring during recording holograms.
  • the cross section area of the illumination at the said 1 st wavelength at a storage location can match the profile of the Object beam through the recording material.
  • a recording material can, by way of example, comprise a uniformly dispersed dye compound, or a dye compound adsorbed to the surface of a particle, such as a nanoparticle or core-shell particle that is dispersed in the material.
  • Said dye compound can be a Near Infrared (NIR) dye or Infrared (IR) dye compound that absorbs NIR or IR light, respectively, or can be a compound that absorbs in the short to middle range of visible wavelengths (i.e.
  • NIR Near Infrared
  • IR Infrared
  • the dye molecule can be part of a larger molecule including chemical structure that undergoes other chemical or photochemical or stereochemical or conformational processes or changes, including, by way of example, changes in molecular or chemical structure such as geometric isomerization and rearrangement, ring opening, ring closure, formation of cyclic products or intermediates including bicyclic products, such as by cycloaddition reactions, wherein said processes or changes, by way of example, can be related to the wavelength and/or intensity of light that illuminates the recording material at the selected location(s) and said processes or changes may, optionally, be reversible or partially reversible between two or more chemical or photochemical or structural states.
  • the recording material includes a compound that can be chemically or structurally altered by exposure of one or more locations in the recording material to UV, or visible, or NIR or IR radiation, or combinations thereof, such as in a stepwise process, or alternatively simultaneously, so as to form the desirable active species during the threshold or activation event for photoinitiation of polymerization or other initiation of polymerization in the recording material at the recording wavelength.
  • Said active species activated dye compound
  • the formation of the active species for photoinitiation of polymerization in the recording material at the recording wavelength can, alternatively, occur due to presence of oxygen, or to reducing or substantially eliminating the presence of oxygen, or to reducing or substantially eliminating the population of other molecule(s) that can act as a retarder(s) or inhibitor(s) to slow or prevent photoinitiation processes for initiating polymerization in the one or more selected locations of the recording material.
  • the compounds that act as a retarder or inhibitor may additionally be diffusible in the recording medium.
  • oxidation/reduction reaction(s) of the compound can occur due to reactions with a suitable photoacid generator that does not form sufficiently strong acid for initiating photopolymerization of siloxy silane epoxy compounds or vinyl ethers and the like.
  • the amount of the in-situ formed absorber species that is formed during or after exposure to said 1 st wavelength can preferably be tuned or controlled to the amount required to achieve suitable recording sensitivity for a particular exposure fluence, or tuned or controlled for the population of monomer that can polymerize in the volume of the interaction volume of the Object and Reference beam wherein the population can change during a sequence of recording events utilizing co-locational multiplexing, or tuned or controlled for the population of other compounds that can participate in the photoinitiation process for polymerization reactions in the said interaction volume, and the like, such as in a sequence of multiplexed holographic recordings.
  • This metering process for in-situ formation of the active compound can be particularly advantageous for achieving high fidelity in thicker recording materials. It can also provide for direct read after write capability, such as may be used for evaluating BER of recorded holograms, and can be advantageous for achieving more uniform recording sensitivity during a sequence of multiplexed recording event, as well as tuning or controlling other holographic performance attributes.
  • compounds for the threshold event can absorb short wavelength radiation, such as UV radiation, that causes chemical structure change and formation of a new compound that absorbs at the recording wavelength or some other visible wavelength that can be additionally be used for illumination of the volume at the selected storage location and thereby create the compound for photoinitiation or other initiation of polymerization at the recording wavelength.
  • short wavelength radiation such as UV radiation
  • the compound formed from the threshold or activation event can optionally be reversibly converted back to the species that is inactive at the recording wavelength, and then converted again by another threshold or activation event to the compound that can photoinitiate or otherwise initiate polymerization during hologram recording.
  • the same optical system, or portions of the same optical system, used for delivering the Object beam to the selected location(s) in the recording material can be used for delivering the irradiation from the said 1st wavelength that is used for activation.
  • a longer 1st wavelength would result in longer focal length due to dispersion of the refractive index of the glass materials used for optics, but the spot sizes would not differ significantly for the two wavelengths for suitable optical designs.
  • a shorter 1 st wavelength would result in shorter focal length due to said dispersion.
  • a separate optical element or optical system or portion of an optical system can be used for delivering the said 1 st wavelength to a storage location for the threshold or activation event.
  • the threshold or activation event can be carried out as part of a servo system, such as used for tracking, addressing and/or alignment, that can optionally interact with the media at locations forward of the recording events such that activation occurs prior to recording.
  • a servo system such as used for tracking, addressing and/or alignment
  • An optical system of the apparatus can be designed advantageously with approximately equal focal lengths for both wavelengths, or to provide for a correction using one or more other optical elements, optionally adaptive optics, so that when the two wavelengths are coupled in the same optical path then the focal distances would be similar for optimizing the similarity of the areas of illumination.
  • FIG. 6 is a plot showing diffraction efficiency, ⁇ , as a function of recording exposure energy E.
  • Diffraction efficiency, ⁇ in a selected location in the recording material does not change and is nominally a value of zero as a function of exposure energy at a recording wavelength ⁇ 2 until an activation event occurs at the selected location at the activation or threshold wavelength X ⁇ . Further, ⁇ , in the selected location in the recording material does not change and is nominally a value of zero as a function of exposure energy at the said activation wavelength ⁇ ⁇ .
  • holographic exposure at the recording wavelength ⁇ 2 can form hologram(s) that exhibit a value of ⁇ that is related to the magnitude of the exposure energy at the recording wavelength X 2 .
  • ⁇ ⁇ and ⁇ El can represent two values of ⁇ achieved for two values of recording exposure energy E a and E b , respectively, in mJ/cm 2 , wherein Eb > E a and the exposure energy E a and Eb occur at the recording wavelength X 2 .
  • the magnitude of exposure in mJ/cm 2 at the activation or threshold wavelength can influence the magnitude of ⁇ achieved at the recording wavelength ⁇ 2 for two values of activation exposure energy E a and E b at the activation wavelength X ⁇ .
  • activation exposure energy at wavelength X ⁇ for purposes of activation at a selected location forms a compound having a population that is sufficient to activate polymerization at wavelength X 2 , but only for recording a portion of the whole dynamic range of the material at the selected location on the basis of the population of monomer that can polymerize if full activation was achieved, then, by way of example, a diffraction efficiency of ⁇ ⁇ ⁇ ⁇ can occur for an energy of E a for the activation or threshold event for the range of exposure energy at the recording wavelength X 2 .
  • the exposure energy at X 1 is E b for the activation or threshold event
  • Eb provides for an activation state at a selected location that is greater than the activation state provided for by E a
  • the formed compound has a population that is insufficient to fully activate polymerization at wavelength ⁇ 2 on the basis of the population of monomer that can polymerize if full activation was achieved
  • a diffraction efficiency of ⁇ ⁇ ⁇ E can occur for an energy of Eb for the activation or threshold event for the range of exposure energy at the recording wavelength ⁇ 2 .
  • Scheme 1 illustrates a general procedure that may be used for the preparation of switch compounds, according to various embodiments.
  • Compounds C and D may be prepared according to the procedure set forth in Macromolecules, (2003), p. 298-303.
  • Compounds H, J, and K may be prepared according to the procedures as set forth in J. Am. Chem. Soc. (2006), pl3680-13681 or Org. Lett. (2003), 3195-3198.
  • Triisopropylsilyl chloride (12.2 mL, 57 mmol) was then added at -78°C and the reaction slowly warmed up to room temperature overnight and stirred for three days. The solvents were removed in vacuo and the solid applied to a silica hexanes column. The fractions were collected and the solvents removed in vacuo. The product was recrystallized from isopropanol and dried under vacuum at 60 0 C. A second recrystallization from isopropanol afforded compound (F) as white crystals (10.0 g, 60% yield; m.p. 58-60 0 C).
  • Switch compound S4 (58 mg, 0.10 mmol), arylboronic acid (0.2 mmol), tris(dibenzylideneacetone) dipalladium(O) (5 mg, 10 mol% Pd), SPhos (9 mg, 20 mol% L)and anhydrous potassium phosphate tribasic (85 mg, 400 mol%) were placed in a dry 3 mL vial with Teflon septum screw cap and evacuated/refilled three times with argon or nitrogen. De-gassed, anhydrous n-butanol (1 ml) was added and the mixture heated overnight at 100 0 C. The reaction mixture was then cooled, the solvent removed in vacuo, and the crude product applied to a silica column packed in hexane.
  • the column was then eluted with a gradient of methylene chloride/hexanes (5% 100 mL, 10% 100 mL, 20% 100 mL). The pure fractions were combined, the solvent again removed in vacuo, and methanol was added to form a slurry. The slurry was transferred to a centrifuge tube and stored in the freezer overnight. The slurry was then centrifuged cold and decanted. The light green solid product was dried under high vacuum to afford ⁇ 25 mg (-40% yield) product. The final structures of the grouping of molecular switch products were confirmed by NMR.
  • Compound S5-a was characterized by 1 HNMR (400 MHz, CDCl 3 ): 1.254, 1.554 (a, b); 1.934, 1.982, 2.491 (1); 6.668, 6.671, 6.677, 6.680 (k); 6.959, 6.967, 6.974, 6.983, 6.999, 7.008 (j, i, h); 7.270 (f); 7.283, 7.302, 7.320 (e); 7.308, 7.388, 7.407 (d); 7.534, 7.553 (c); where the protons are assigned as:
  • Compound S5-b was characterized by 1 HNMR (400 MHz, CDCl 3 ): 1.935, 1.962 (a, b); 2.489, 2.490 (1); 3.837 (c); 6.667. 6.670, 6.676, 6.679 (k); 6.903, 6.925 (e); 6.958, 6.966, 6.972, 6.982, 6.996, 7.005 (j, i, h); 7.109 (g); 7.144 (f); 7.454, 7.476 (d); where the protons are assigned as:
  • Compound S5-c was characterized by 1 HNMR (400 MHz, CDCl 3 ): 1.964, 2.0303 (a, b); 2.488 and 2.491 (k); 6.669, 6.672, 6.678, 6.681 (j); 6.957, 6.996 (i); 6.976, 6.985 (h); 7.001, 7.011 (g); 7.090 (f); 7.402 (e); 7.791, 7.923 (d); where the protons are assigned as:
  • Asymmetric switch compounds may be prepared according to the example provided by Scheme 2.
  • the symmetric molecular switch compounds S8a/b with acetylene linking groups to the switch core were prepared following the general procedure below. [0143] A reaction vessel equipped with a stir bar was charged with S6 (100 mg, 0.19 mmol), ethynylarene ( 0.47 mmol), triphenylphosphine (22 mg, 0.08 mmol), tris(dibenzylideneacetone)dipalladium(0) (8 mg, 0.009 mmol), and copper(I) iodide (32 mg, 0.17 mmol). The vessel was fitted with a Teflon-septum screw cap and evacuated/refilled three times with nitrogen.
  • a polymerizable formulation was prepared including the photo- sensitizer DMTT, 0.032%, and Rhodorsil PI2074, 4.8% in Diepoxy monomer PClOOO.
  • the sensitization properties of DMTT for initiating cationic polymerization were evaluated using calorimetry (PDSC) as described below.
  • Cationic ring-opening polymerization is an exothermic process, therefore polymerization rates and extents of monomer conversion can be determined through calorimetry.
  • Calorimetric analysis was performed on a Perkin- Elmer DSC-7 Differential Scanning Calorimeter equipped with an integrated DPC-7 Photocalorimeter Module including a medium pressure IOOW Hg lamp, transfer optics and a monochromator to control the wavelength of light exposure. Samples, 1.5-2.5 mg, were weighed into a standard DSC sample pan, placed into the calorimeter sample chamber and equilibrated at 30 0 C prior to illumination.
  • q(t) is the heat evolved after illumination time t
  • ⁇ H rxn the heat of light- induced reaction
  • 407nm light are indicative of fast reaction kinetics, and are shown in FIG. 9.
  • the onset of polymerization was determined to be at 2.032 min, corresponding to 0.032 min after the shutter opens. Peak enthalpy is achieved at 2.052 min, or 0.052 min after the shutter opened.
  • the polymerization reaction is complete by 0.1 min (6 seconds), equal to 25.2 mJ/cm 2 exposure energy, with little or no further enthalpy of reaction realized with further light exposure.
  • a sample of molecular switch dye compound S7 which includes a substituted thiophene dye grouping was dissolved in dichloromethane (DCM). Exposure of the open form, S7-open, in DCM solution to UV light (from an LED source), caused the compound to undergo a molecular switch to the "closed" form, S7-closed.
  • the closed molecular switch dye compound S7-closed has a ⁇ max at 568 nm.
  • a stock Dye formulation was prepared from S7-open (9.73mg) and enough diepoxydisiloxane to make 4.98893g of a stock formulation having 0.195 wt% of S7-open in the diepoxydisiloxane.
  • a magnetic stir bar was added, stirring commenced and the stock Dye formulation was subjected to irradiance from UV light for 20 min from an LED source. The color of the Dye formulation changes upon exposure to light of 386 nm to dark blue, yielding a stock formulation including S7-closed.
  • v and w total 4, 5, or 6, was charged to a vessel equipped with a magnetic stir bar.
  • a difunctional epoxide monomer of formula R'- Si(RR)-O-Si(RR)-R' where each group R' is a 2-(3,4-epoxycyclohexyl)ethyl grouping; and each grouping R is a methyl group, and which is available from Polyset Corporation, Inc., Mechanicsville, NY., under the trade name PC-1000.
  • the ratio of the binder to the di-functional monomer was 1. :46: 1.0.
  • the mixture of binder and di-functional monomer was stirred to form a uniform homogeneous mixture.
  • C8 tetramer a poly-functional monomer, referred to herein as C8 tetramer (see compound No. XXII US 6,784,300), in a ratio of 1.12:1 multifunctional epoxy to difunctional monomer, and the contents were stirred at room temperature to form a uniform mixture of a stock CROP formulation (SCF).
  • SCF stock CROP formulation
  • S5c 1.4 mg was added to enough SCF to make 0.6832 g of a new formulation comprising S5c at approximately 0.2%, SCF-Dye-open.
  • This formulation was irradiated with UV light (LED source) for 6 hours to fully convert S5c to the closed form to yield SCF-Dye-closed.
  • a second formulation was then prepared using SCF, and Rhodorsil PAG to make a formulation of 4.5% PAG in SCF.
  • the SCF-Dye-closed was added to the 4.5% PAG in SCF formulation to yield a CROP formulation with -0.03% S5c-closed.
  • the formulation was then filtered using an Acrodisc® CR25 mm Syringe filter with a 0.2 micron PTFE Membrane into an appropriate size storage container.
  • a card type media was prepared by first fixing two flat glass substrates disposed in a parallel, co-planar arrangement with a space or gap of 100 microns between the inner surfaces of the top and bottom substrates. Examples of methods for media assembly can be found in US 6,881,464. The formulation was coated between the two substrates using capillary forces. After complete filling of the "gap" the media was ready for further analysis.
  • the recording times of the schedule for recording the nine multiplexed holograms was consistent with recording energies used to record holograms in STX Aprilis Type D DHD® media of the same thickness for attaining moderately strong ( ⁇ 5% to -30%) diffraction efficiency for a small number of multiplexed holograms.
  • the intensities of the two writing beams at the condition of equal semiangles about the normal to the sample were 2.3 and 2.5 mW/cm , and the total incident intensity for recording was 4.85 mW/cm 2 as measured at the bisecting condition.
  • the recording times used were consistent with those conventionally used for multiplexing a similar number of plane wave volume holograms in STX Aprilis Type E DHD® media, [see D.A. Waldman, E.S. KoIb, and C. Wang, "DHD® CROP Holographic Storage Media for Advanced Optical Data Storage", Optical Data Storage (ODS), OSA Technical Digest Series, WDPD, 4-7 (2007)]. No evidence of hologram formation was detected.
  • Holographic recording at 407 nm using a Sony diode laser equipped with a temperature controlled external cavity, was carried out in the activated storage location of media using planar angle multiplexing methods with collimated signal and reference beams having intensity of 4 and 3.5 mW/beam.
  • the observed diffraction efficiency for 3 multiplexed holograms was 34.0, 33.5 and 42.8 %, respectively, corresponding to a recording sensitivity of 2.1, 1.98 and 2.0 cm/J respectively.
  • a comparative recording of holograms was carried out on different selected location B in the media, wherein location B was not firstly exposed to actinic radiation at a first wavelength (532 nm) for activation.
  • Holographic recording at 407 nm was carried out in the non activated storage location of the media as above.
  • the observed diffraction efficiency for 3 multiplexed holograms was 7.6, 10.6 and 16.8 %, respectively, corresponding to a recording sensitivity of 0.97, 1.11 and 1.27 cm/J respectively, that are only diminished compared to the activated location.
  • the holographic recording media exhibited substantially no recording sensitivity to exposure in the material at the recording second wavelength ( ⁇ 2 ) without having firstly forming the activated photosensitizer molecular switch compound by use of a first exposure at a first activation wavelength (X 1 ).
  • this high level of selectivity allows for the recording of holograms in a sensitized location in the media, without risk of loss of recording dynamic range in adjacent locations due, e.g., to spillover of recording (e.g. object or reference beam) light at the recording second wavelength ( ⁇ 2 ).
  • the minimum pumping exposure energy at the activation wavelength ⁇ ⁇ required to form the activated photosensitizer molecular switch compound was not determined, so an extensive exposure time of 10 minutes was used as a default condition for activation of the photosensitizer molecular switch compound.
  • Co-locational slant fringe plane-wave transmission volume holograms were recorded at the second wavelength, ⁇ 2 , in the conventional manner with a Sony Corp SBL single longitudinal mode blue-purple diode laser model emitting at 407 nm using two coherent spatially filtered and collimated laser writing beams directed onto the sample with an interbeam angle of 51.3°.
  • the intensities of the two writing beams at the condition of equal semiangles about the normal were 2.3 and 2.5 mW/cm 2 , and the total incident intensity for recording was 4.85 mW/cm 2 as measured at the bisecting condition.
  • Diffraction efficiency data was obtained at angle increments of 0.02° over an angle sweep of +/- 2.0° from the respective recording angles of each hologram using two model 818-SL/CM photodiodes and a model 2835-C dual channel multi-function optical meter from Newport Corporation for measuring the primary diffracted intensity, I 1 , and the transmitted non diffracted intensity, I 0 .
  • the measured diffraction efficiency, ⁇ t was obtained at the peak of the Bragg selectivity profile of the ith recorded hologram in a storage location in the recording material in accordance with
  • T thickness of the recording material
  • U is the length of the recording time for the zth recording event
  • I 1 is the intensity for the recording event of the zth multiplexed hologram. Recording sensitivities were moderately high at 3.25, 3.56, 3.93, 3.51, 3.47, 3.07, 0.73, 0.67 and 0.49 cm/mJ for the co-locationally multiplexed volume holograms #l-#9, respectively.
  • ⁇ is the wavelength at which the hologram is recorded or reconstructed
  • ⁇ is the internal incidence angle of the Reference beam for reconstruction of the recorded hologram
  • m is the amplitude of the refractive index modulation of the hologram
  • M is the number of co-locationally multiplexed volume holograms
  • T is the thickness of the recording material
  • the growth in cumulative grating strength exhibits a linear ramp with increasing cumulative recording energy, and the recording sensitivity declines and then exhibits a fairly flat dependence with further increases in cumulative recording energy, thereby indicating that the recording chemistry of the activated media was not fully consumed during the recording schedule used for the co-locationally multiplexed volume holograms.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Holo Graphy (AREA)

Abstract

La présente invention concerne un support polymérisable qui comprend un support d'enregistrement holographique. Le support comprend au moins un monomère ou un oligomère qui subit une polymérisation; un composé, qui absorbe le rayonnement actinique d'une première longueur d'onde et forme un sensibilisateur qui absorbe le rayonnement actinique d'une seconde longueur d'onde; et un initiateur, qui, en association avec le sensibilisateur, initie la polymérisation du ou des monomères ou oligomères lorsque ledit sensibilisateur est exposé au rayonnement actinique de la seconde longueur d'onde.
PCT/US2010/027466 2009-03-16 2010-03-16 Procédé de contrôle d'activation d'une photopolymérisation pour le stockage de données holographiques à l'aide d'au moins deux longueurs d'onde WO2010107784A1 (fr)

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WO2021040825A1 (fr) * 2019-08-23 2021-03-04 Facebook Technologies, Llc Modification de modulation d'indice de réfraction dans un réseau holographique
CN114207532A (zh) * 2019-08-23 2022-03-18 脸谱科技有限责任公司 全息光栅中的折射率调制修改
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