Holographic optical elements having a reflection hologram formed in a photopolymer

Claim 2

A holographic optical element comprising a transparent polymeric film containing a reflection hologram, said film having a refractive index modulation greater than approximately 0.001 and being formed by exposing to coherent light a composition consisting essentially of: (a) approximately 25 to 90% of a polymeric binder selected from the group consisting of polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl formal, interpolymers containing major segments thereof, and mixtures thereof; (b) approximately 5 to 60% of an ethylenically unsaturated monomer selected from the group consisting of carbazole containing monomers and a liquid monomer containing one or more phenyl, biphenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic group containing up to three aromatic rings, chlorine and bromine; (c) approximately 0 to 25% of a plasticizer; and (d) approximately 0.1 to 10% of a photoinitiator system activatable by actinic radiatio wherein said percentages are weight percentages based on total film weight.

Claim 3

The element of claim 1 wherein the film has a reflection efficiency of at least approximately 15%.

Claim 4

The element of claim 2 mounted on a transparent substrate.

Claim 5

The element of claim 1 wherein said film has a thickness of approximately 1 to 100 micrometers and

Claim 6

a refractive index modulation greater than approximately 0.005.

Claim 7

a refractive index modulation greater than approximately 0.005.

Claim 8

The element of claim 4 wherein said film has a reflection efficiency of at least approximately 70%.

Claim 9

The element of claim 1 wherein the ethylenically unsaturated monomer is a liquid selected from the group consisting of phenoxyethyl acrylate, phenol ethoxylate monoacrylate, the di(2-acryloxyethyl) ether of bisphenol-A, ethoxylated bisphenol-A diacrylate, 2-(1-naphthyloxy) ethyl acrylate, ortho-biphenyl methacrylate, and mixtures thereof.

Claim 10

The element of claim 1 wherein the ethylenically unsaturated monomer is a mixture of a solid monomer selected from the group consisting of N-vinyl carbazole; 3,6-dibromo-9-vinyl carbazole; 2,4,6-tribromophenyl acrylate or methacrylate; pentachlorophenyl acrylate or methacrylate; 2-vinyl naphthalene; 2-naphthyl acrylate or methacrylate; 2-(2-naphthyloxy)ethyl acrylate or methacrylate; para-biphenyl methacrylate; t-butylphenyl methacrylate, the di-(2-acryloxyethyl)ether of tetrabromo-bisphenol-A and mixtures thereof; and a liquid monomer selected from the group consisting of phenoxyethyl acrylate; phenol ethoxylate acrylate; the di(2-acryloxyethyl ether) of bisphenol-A; ortho-biphenyl methacrylate; ethoxylated bisphenol-A diacrylate: 2-(1-naphthyloxy)ethyl acrylate, and mixtures thereof.

Claim 11

The element of claim 1 containing a plasticizer selected from the group consisting of tris(2-ethylhexyl)phosphate, glyceryl tributyrate, and a compound having the general formula: or wherein R, and R 2 each is an alkyl group of 1 to 10 carbon atoms, R 3 is H or an alkyl group of 8 to 16 carbon atoms, R 4 is H or CH 3 , x is 1-4, y is 2-20, and z is 1-20.

Claim 12

The element of claim 8 wherein the plasticizer is selected from the group consisting of triethylene glycol dicaprylate, triethylene glycol bis(2-ethylhexanoate), diethyl adipate, dibutyl adipate, tetraethylene glycol diheptanoate. dibutyl suberate, diethyl sebacate, tris(2-ethylhexyl)phosphate, and glyceryl tributyrate.

Claim 13

The element of claim 1 wherein the composition contains up to approximately 5% optional ingredients.

Claim 14

The element of claim 1 wherein the components in said composition are present in the following approximate weight ranges: binder. 45 to 75%; monomer, 15 to 50%; plasticizer, 0 to 15%; initiator. 1 to 5%; and optional components, 0 to 4°0; and said film has a refractive index modulation of at least approximately 0.005.

Claim 15

The element of claim 11 wherein said film has a thickness of approximately 1 to 100 micrometers.

Claim 16

The element of claim 12 wherein the film has a reflection efficiency of at least approximately 70%

Claim 17

The element of claim 11 wherein the film has a refraction index modulation of at least approximately 0.01.

Claim 18

In a process for forming a reflection hologram wherein a reference beam of coherent actinic radiation and an object beam of the same coherent actinic radiation enter a layer of recording medium from opposite sides to create an interference pattern in the medium that forms the hologram, the improvement wherein the medium is a substantially solid, photopolymerizable layer consisting essentially of: (a) a polymeric binder selected from the group consisting of polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl formal, interpolymers containing major segments thereof, and mixtures thereof; (b) an ethylenically unsaturated monomer selected from the group consisting of carbazole containing monomers and a liquid monomer containing one or more phenyl, biphenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic group containing up to three aromatic rings, chlorine and bromine and (c) a photoinitiator system activatable by the actinic radiation and the resulting imaged medium has a refractive index modulation of at least approximately 0.001.

Claim 19

In a process for forming a reflection hologram wherein a reference beam of coherent actinic radiation and an object beam of the same coherent actinic radiation enter a layer of recording medium from opposite sides to create an interference pattern in the medium that forms the hologram, the improvement wherein the medium is a substantially solid, photopolymerizable layer consisting essentially of: (a) a polymeric binder selected from the group consisting of polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl formal, interpolymers containing major segments thereof, and mixtures thereof; (b) an ethylenically unsaturated monomer selected from the group consisting of carbazole containing monomers and a liquid monomer containing one or more phenyl, biphenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic group containing up to three aromatic rings, chlorine and bromine and (c) a photoinitiator system activatable by the actinic radiation and the resulting imaged medium has a refractive index modulation of at least approximately 0.001.

Claim 20

The process of claim 15 wherein the liquid monomer is selected from the group consisting of phenoxyethyl acrylate, phenol ethoxylate monoacrylate, the di(2-acryloxyethyl) ether of bisphenol-A, ethoxylated bisphenol-A diacrylate, 2-(1-naphthyloxy) ethyl acrylate, ortho-biphenyl methacrylate, and mixtures thereof.

Claim 21

The process of claim 15 wherein the ethylenically unsaturated monomer is a mixture of a solid monomer selected from the group consisting of N-vinyl carbazole; 3,6-dibromo-9-vinyl carbazole; 2,4,6-tribromophenyl acrylate or methacrylate; pentachlorophenyl acrylate or methacrylate; 2-vinyl naphthalene; 2-naphthyl acrylate or methacrylate; 2-(2-naphthyloxy)ethyl acrylate or methacrylate; para-biphenyl methacrylate; t-butylphenyl methacrylate, the di-(2-acryloxyethyl)ether of tetrabromo-bisphenol-A and mixtures thereof; and a liquid monomer selected from the group consisting of phenoxyethyl acrylate; phenol ethoxylate acrylate; the di(2-acryloxyethyl ether) of bisphenol-A: ortho-biphenyl methacrylate; ethoxylated bisphenol-A diacrylate; 2-(1-naphthyloxy)ethyl acrylate; and mixtures thereof.

Claim 22

The process of claim 15 in which a plasticizer is also present, which plasticizer is selected from the group consisting of tris(2-ethylhexyl)phosphate, glyceryl tributyrate. and a compound having the general formula: or wherein R, and R 2 each is an alkyl group of 1 to 10 carbon atoms, R 3 is H or an alkyl group of 8 to 16 carbon atoms, R 4 is H or CH 2 , x is 1-4, y is 2-20, and z is 1-20.

Claim 23

The process of claim 18 wherein the plasticizer is selected from the group consisting of triethylene glycol dicaprylate, triethylene glycol bis(2-ethylhexanoate), diethyl adipate, dibutyl adipate, tetraethylene glycol diheptanoate, dibutyl suberate, diethyl sebacate, tris(2-ethylhexyl)phosphate, and glyceryl tributyrate.

Claim 24

The process of claim 18 in which said plasticizer is substituted for at least a portion of the liquid ethylenically unsaturated monomer.

Claim 25

The process of claim 15 wherein the solid photopolymerizable layer contains an added crosslinking monomer containing two or more terminal ethylenically unsaturated groups.

Claim 26

The process of claim 21 wherein the crosslinking monomer is diacrylate or dimethacrylate of a bisphenol-A epoxy adduct.

Claim 27

A process for forming a reflection hologram in a substantially solid photopolymerizable recording medium comprising: A. Projecting a reference beam of coherent actinic radiation on a first side of the recording medium which consists essentially of:

Claim 28

A process for forming a reflection hologram in a substantially solid photopolymerizable recording medium comprising: A. Projecting a reference beam of coherent actinic radiation on a first side of the recording medium which consists essentially of:

Claim 29

(1) a polymeric binder selected from the group consisting of polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl formal, interpolymers containing major segments thereof and mixtures thereof:

Claim 30

(1) a polymeric binder selected from the group consisting of polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl formal, interpolymers containing major segments thereof and mixtures thereof:

Claim 31

(2) an ethylenically unsaturated monomer selected from the group consisting of carbazole containing monomers and a liquid monomer containing one or more phenyl, biphenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic group containing up to three aromatic rings, chlorine and bromine and

Claim 32

(2) an ethylenically unsaturated monomer selected from the group consisting of carbazole containing monomers and a liquid monomer containing one or more phenyl, biphenyl, phenoxy, naphthyl, naphthyloxy, heteroaromatic group containing up to three aromatic rings, chlorine and bromine and

Claim 33

(3) a photoinitiator system activatable by the actinic radiation; B. Concurrently projecting an object beam of the same coherent actinic radiation approximately in an opposite direction to the reference beam onto a second side of the photopolymerizable layer so as to intersect with the reference beam in a plane within the layer whereby a reflection hologram is formed; C. Irradiating the imaged photopolymerizable layer with uniform source of actinic radiation; said resulting imaged medium having a refractive index modulation of at least approximately 0.001.

Claim 34

(3) a photoinitiator system activatable by the actinic radiation; B. Concurrently projecting an object beam of the same coherent actinic radiation approximately in an opposite direction to the reference beam onto a second side of the photopolymerizable layer so as to intersect with the reference beam in a plane within the layer whereby a reflection hologram is formed; C. Irradiating the imaged photopolymerizable layer with uniform source of actinic radiation; said resulting imaged medium having a refractive index modulation of at least approximately 0.001.

Claim 35

The process of claim 23 including the step, after step C, of treating the irradiated layer with a liquid enhancing agent to increase the medium refractive index modulation to at least approximately 0.005.

Claim 36

The process of claim 24 wherein the liquid enhancing agent contains an organic liquid selected from the group consisting of an alcohol, a ketone, an aldehyde, a glycol alkyl ether, an ester, a liquid monomer and mixtures thereof.

Claim 37

The process of claim 25 wherein the liquid enhancing agent is selected from the group consisting of 1-propanol, methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone, cyclohexanone, benzaldehyde, ethyl acetate, butyl benzoate, phenoxyethyl acrylate, phenol ethoxylate acrylate, ethoxylated bisphenol-A diacrylate, and mixtures thereof.

Claim 38

The process of claim 24 wherein the liquid enhancing agent contains a substantially inert liquid diluent.

Claim 39

The process of claim 24 wherein the liquid diluent is selected from the group consisting of water, inert hydrocarbon solvents, 1,2-dichloroethane, and trichlorotrifluoroethane.

Claim 40

The process of claim 25 wherein swelling agent is removed from the treated layer by evaporation.

Claim 41

The process of claim 24 including the step of sealing the liquid enhancing agent in the recording medium.

Claim 42

The process of claim 24 wherein the liquid enhancing agent is a monomer, and including the additional steps of contacting the irradiated recording medium with liquid monomer that is absorbed by the medium, drying the medium to remove excess monomer, and polymerizing the absorbed monomer by exposure to actinic radiation.

Claim 43

The process of claim 31 wherein said treatment with liquid monomer is performed after the medium has been heated to a temperature above 50 C to enhance reflection efficiency.

Claim 44

The process of claim 24 including the step of heating the medium, after it has been exposed to coherent radiation to form a reflection hologram, to a temperature of at least approximately 50°C for a sufficient period to enhance the refractive index modulation to at least approximately 0.005.

Claim 45

The process of claim 33 wherein the medium is heated to a temperature in the range of approximately 80 to 160°C.

Claim 46

The process of claim 34 wherein said thermal enhancement step is conducted after step C.

Claim 47

The process of claim 23 wherein the recording medium is preheated immediately prior to exposing the medium to coherent radiation during steps A and B.

Claim 48

The process of claim 36 wherein the recording medium is preheated to approximately 30' to 50' C.

Claim 49

The process of claim 23 wherein the solid recording medium also contains crosslinking monomer containing at least two terminal ethylenically unsaturated groups.

Claim 50

The process of claim 38 wherein the crosslinking monomer is diacrylate or dimethacrylate of a bisphenol-A epoxy adduct.

Claim 51

The process of claim 23 wherein the unsaturated monomer is phenoxyethyl acrylate, phenol ethoxylate monoacrylate, the di(2-acryloxyethyl) ether of bisphenol-A, ethoxylated bisphenol-A diacrylate. 2-(1-naphthyloxy) ethyl acrylate, ortho-biphenyl methacrylate, and mixtures thereof.

Claim 52

A process of claim 23 wherein the ethylenically unsaturated monomer is a mixture of a solid monomer selected from the group consisting of N-vinyl carbazole; 3,6-dibromo-9-vinyl carbazole; 2,4,6-tribromophenyl acrylate or methacrylate; pentachlorophenyl acrylate or methacrylate; 2-vinyl naphthalene; 2-naphthyl acrylate or methacrylate; 2-(2-naphthyloxy)ethyl acrylate or methacrylate; para-biphenyl methacrylate; t-butylphenyl methacrylate, the di-(2-acryloxyethyl)ether of tetrabromo-bisphenol-A, and mixtures thereof; and a liquid monomer selected from the group consisting of phenoxyethyl acrylate; phenol ethoxylate acrylate; the di(2-acryloxyethyl ether) of bisphenol-A; ortho-biphenyl methacrylate; ethoxylated bisphenol-A diacrylate; 2-(1-naphthyloxy)ethyl acrylate; and mixtures thereof.

Claim 53

The process of claim 23 in which a plasticizer is also present, which plasticizer is selected from the group consisting of tris(2-ethylhexyl)phosphate, glyceryl tributyrate, and a compound having the general formula: or wherein R, and R 2 each is an alkyl group of 1 to 10 carbon atoms, R 3 is H or an alkyl group of 8 to 16 carbon atoms, R 4 is H or CH 3 , x is 1-4, y is 2-20, and z is 1-20.

Claim 54

The process of claim 42 wherein the plasticizer is selected from the group consisting of triethylene glycol dicaprylate. triethyleneglycol bis(2-ethylhexanoate), diethyl adipate, dibutyl adipate, tetraethylene glycol diheptanoate, dibutyl suberate, diethyl sebacate, tris(2-ethylhexyl)phosphate. and glyceryl tributyrate.

Claim 55

The process of claim 42 in which said plasticizer is substituted for a portion of the liquid ethylenically unsaturated monomer.