Holographic recording material

Details Holographic recording material Holographic recording material

1999-10-12

2002-02-05

Angebranndt, Martin (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Holographic process, composition, or product

Composition or product or process of making the same

C430S001000, C359S003000

Reexamination Certificate

active

06344297

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to holographic recording materials (HRMs) having a polymer matrix and a light harvesting dye.
BACKGROUND OF THE INVENTION
The fundamental aspect of an HRM is to utilize a photochemical phenomenon wherein the light harvesting dye absorbs light, reacts with the polymer matrix, and alters the index of refraction. These induced refractive index modulations result in phase holograms with high diffraction efficiency and angular selectivity. Previous HRMs are well known, but the HRM closest to the subject invention is limited to a poly(methyl methacrylate) (PMMA) polymer and a light harvesting dye, 9,10-phenanthrenequinone composite.
For example, A. Popov et al. (A. P. Popov, A. V. Veniaminov, Y. N. Sedunov,
SPIE
2215, 64, 1994) describe a general method of fabricating a 6 to 8 mm thick HRM having a gradient distribution of the 9,10-phenanthrenequinone dye in the PMMA matrix across the material's thickness. The highest dye concentration is in the center of the HRM's cross-section and the lowest at each surface. This variation of the dye concentration is achieved by exposing each surface to a mercury lamp light filtered in such a way that the transmission maximum coincides with having a wavelength within the absorption profile of 9,10-phenanthrenequinone dye. As the light propagates through the HRM, its intensity falls exponentially with the penetration depth in accordance with the Lambert-Beer law. The accompanying photoinduced effect, a reaction between the dye and the polymer matrix, decreases. Thereby, unreacted dye is located toward the center of the HRM's cross-section.
In the same publication, Popov et al. describe another method of fabricating a thick HRM with a gradient distribution of the 9,10-phenanthrenequinone dye in a PMMA matrix. In this method, the initial 100 micrometers thick layer of PMMA polymer is doped with 10 wt % of 9,10-phenanthrenequinone, which was prepared from a dichloroethane solution. The dried film was then placed between two 3 mm thick pure PMMA slabs and entire assembly pressed together and heated to accelerate dye diffusion from the center layer to outside layers. The diffusion into the PMMA slabs depends on the temperature. In most instances, the temperature exceeds the PMMA's glass transition temperature. Obviously, this result is not desired.
Likewise, B. Ludman et al. (J. E. Ludman, N. O. Reinhard, I. V. Semenova, Yu. L. Korzinin, and S. M. Sahriar,
SPIE
2532, 481, 1995) describe the use of a HRM consisting of 0.5 to 5 wt % of 9,10-phenanthrenequinone in a PMMA matrix. This HRM has similar problems of Popov et al.
Similarly, C. Steckman et al. (G. J. Steckman, I. Solomatine, G. Zou and D. Psaltis,
Opt. Lett
. 23, 1310, 1998) describe the preparation of a 1 to 5 mm HRM comprising 0.7 wt % of 9,10-phenanthrenequinone dye dissolved in a PMMA matrix. To prepare such material, a solution of the dye, a polymerization initiator, and methyl methacrylate, is poured into molds and allowed to polymerize in a pressure chamber at elevated temperatures.
A problem with these prior references is that the PMMA has a relatively low glass transition which can lead to distortions after light exposure. Another problem is that post exposure treatment at elevated temperatures (around and above the glass transition temperature), significantly reduces the photoinduced index modulation by the diffusion of the photoproducts and, consequently, the strength of the holograms substantially decreases. Another problem relates to the low number of reactive sites in the polymer matrix during holographic recording. Yet another problem involves the limited chemical inertness of the PMMA matrix toward common chemical agents such as alcohols, and acetone.
SUMMARY OF THE INVENTION
The problems of these references can be solved with the present invention. The present invention provides high optical quality HRMs with high holographic storage capacity, thermal stability at elevated temperatures, hardness and inertness toward chemical agents. The present invention is directed to a HRM having at least two distinct acrylate materials and a light harvesting dye. Along with this composition, the present invention is directed to a new method of producing HRM with gradient distribution of the light harvesting dye. This new method results in a HRM with better angular selectivity and optical quality (low scattering).
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a HRM having at least two distinctive acrylate materials and a light harvesting dye, wherein the acrylate materials polymerize. The term “distinctive” means the acrylate material has a secondary carbon chain of a different length. Moreover, each acrylate material is a monomer represented by the structural formulas 1 to 4.
Formula 1 has the following structure:
wherein R′=H; or an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms; or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms; and
R=an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms; or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms.
Formula 2 has the following structure:
R
2
″—O—R—O—R
1
″
wherein R=an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms; or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms; and
R
1
″ and R
2
″=—OC(═O)C(R
3
)═CH
2
or H wherein R
3
=H; or an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms; or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms.
Formula 3 has the following structure:
wherein R=a tri- or tetra-substituted aryl group; or a carbon atom;
R′=H; or an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms; or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms; and
R
1
, R
2
, and R
3
=—OC(═O)C(R
4
)=CH
2
or H
wherein R
4
=H; or an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms; or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms.
Formula 4 has the following structure:
wherein R=a tri- or tetra-substituted aryl group; or a carbon atom;
R′=H; or an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms; or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms;
R
1
′=R
2
′=R
3
′=—CH
2
CH— or —CH
2
CH
2
CH
2
—, and
R
4
′=R
5
′=R
6
′=—OC(═O)C(R
7
′)═CH
2
or H
wherein R
7
′=H; or an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms; or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms.
The light harvesting dye can be a compound or a mixture of two or more dye compounds. The dye compounds must, however, contain at least one of the following structures, labeled as Formulas 5 and 6.
Formula 5 has the following structure:
wherein R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
is an H, R
9
, or X;
R
9
is an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms, or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms; and
X is a halogen.
And Formula 6 has the following structure:
wherein R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, R
8
, is an H, R
9
, or X;
R
9
is an alkyl group, substituted or unsubstituted, having 1 to 8 carbon atoms, or an aryl group, substituted or unsubstituted, having 4 to 20 carbon atoms;
X is a halogen;
When the acrylate materials are polymerized, the polymerized acrylate remains thermally stable at elevated temperatures (about 170° C.), inert toward common chemicals, hard, and light sensitive.
The acrylate materials form a polymer matrix by a free radical polymerization. For this invention to perform as desired, each “at least two distinctive polymerizable acrylic materials” must be distinctive, as defined above. Accor

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