Holographic Photopolymer Materials Research Articles

Monochrome and two-color holograms in layered photopolymer materials

The layered systems of holographic photopolymer materials for recording color holograms are designed and developed. Monochrome and two-color (green-red, red-blue, and green-blue) volume reflection holograms are obtained using the He—Ne, Ar+, and DPSS lasers in red, green, and blue spectral ranges. The effects of cross-bleaching of the dyes used and the holographic properties of monochrome and two-color holograms in layered systems are considered. It is shown experimentally that the diffraction efficiency of these holograms is ~(70–80%) and comparable with that of monochrome holograms obtained in single-layer holographic photopolymer materials.

Photopolymer material sensitized by xanthene dyes for holographic recording using forbidden singlet–triplet electronic transitions

A new holographic photopolymer material is developed. The photopolymer material is sensitized by dyes of xanthene and thioxanthene series which contain iodine and bromine heavy atoms. Holographic recording was carried out during excitation of forbidden singlet–triplet electron transitions of dyes. Thioerythrosin triethylammonium was identified as the most effective sensitizer among a number of tested dyes. The spectral absorption area of the singlet–triplet electronic transition of the dye is conveyed in the red spectral range from 600 to 700 nm. The sensitivity of the photopolymer material to radiation with 633 nm wavelength is 180 mJ cm−2. Optimization of concentration of the main components of the photopolymer compositions was carried out in order to achieve maximum efficiency of holographic recording.

Method for determining the shrinkage parameters of holographic photopolymer materials

A method has been developed to determine the shrinkage parameters of holographic photopolymer materials (including changes in the mean refractive index and thickness of the recording layer) during hologram recording with a measurement error acceptable for practical applications of these materials. Experimental verification of the method has proved its efficiency.

Effect of glycerol on a diacetone acrylamide-based holographic photopolymer material

The composition of the low-toxicity, environmentally compatible diacetone acrylamide (DA) photopolymer has been modified with the inclusion of different additives. The addition of glycerol to the photopolymer composition is described. Results show that the incorporation of glycerol results in a uniform maximum refractive-index modulation for recording intensities in the range of 1-20 mW/cm(2). This may be attributed to glycerol's nature as a plasticizer, which allows for faster diffusion of an unreacted monomer within the grating during holographic recording. An optimum recording intensity of 0.5 mW/cm(2) is observed for exposure energies of 20-60 mW/cm(2). The modified photopolymer achieves a refractive-index modulation of 2.2×10(-3), with diffraction efficiencies up to 90% in 100 μm layers. Glycerol has also shown to reduce the rate of photobleaching of the DA photopolymer. This is possibly due to more prevalent inhibition effects caused by increased oxygenation of the photopolymer layers. The stability of the photopolymer samples is also improved with the addition of glycerol.

Methods for investigation of holographic photopolymer materials

Results obtained by the authors on the development of holographic methods for investigation of photopolymer materials are presented. The work considers the methods for pulse recording of dynamic transmission gratings and characterization of hologram angular selectivity, the double-beam method of twophoton holographic recording, and heterodyne detection of inhomogeneities in volume holograms.

Sensitization of photopolymer materials by halogenated derivatives of xanthene and thioxanthene dyes in the pulsed recording mode

A holographic photopolymer material based on a poly(vinyl alcohol) matrix, the acrylamide monomer, and triethanolamine as an initiator was sensitized by the xanthene dyes erythrosine; thioeryth-rosine; eosin; thioeosin; thiofluorescein, 4-iodo-, 4,5-diiodo-, and 2,4,5-triiodofluorescein; and 4-bromo-, 4,5-dibromo-, and 2,4,5-tribromothiofluorescein. The quantum yields of photobleaching of these dyes in the polymer matrix were determined. Transmission phase gratings were recorded in the pulse mode (λ = 532 nm, tp = 10 ns). The levels of the diffraction efficiency of holograms were measured, and the 4-bromo- or 4,5-dibromothiofluorescein-triethanolamine system was found to be the most effective photoinitiator.

Diffraction interferometer for studying refractive index dynamics

An experimental assembly is created and a method for simultaneous studying dynamics of phototransformation of holographic photopolymer materials by spectrophotometric and interferometric methods is elaborated. A special diffraction interferometer with combined branches is developed. The interferometer ensures the sensitivity to the change in the refractive index Δn ∼ 10−3 for ∼100 μm specimens.

Optimal optical density of the absorbing holographic materials

The theoretical and experimental estimations of optimal optical density of absorbing holographic photopolymer materials for different schemes of holograms recording are carried out. The estimations are based on analytical equations for dependence of the rate photoinduced change of refractive index and effective thickness of the volume holograms on the initial optical density of the photopolymer. Good accordance of theoretical curves and experimental data is observed. The optimal optical density for material with direct chromophore phototransformation is discussed.

Production and properties of holographic photopolymeric material in a hybrid sol-gel matrix

This paper describes a method of obtaining a holographic photopolymer material 0.5-1 mm thick in a hybrid organic-inorganic matrix and the results of investigating it as a recording medium of 3D holographic memory, as well as for fabricating templates of 2D and 3D photonic crystals. To obtain such a material, a copolymer of vinylpyrrolidone with triethoxyvinylsilane was synthesized, followed by hydrolytic condensation of the given copolymer with tetraethoxysilane presol. It is shown that a solid sol-gel matrix that is stable against cracking can be formed with a presol:copolymer weight ratio of 1:4.

Holographic photopolymer materials: nonlocal polymerization-driven diffusion under nonideal kinetic conditions

The kinetics of photosensitive polymer holographic recording materials are examined assuming a material that exhibits nonideal kinetic behavior. Previously, a linear relationship between monomer concentration and polymerization was assumed when deriving the nonlocal polymer-driven diffusion (NPDD) model. This is consistent with ideal kinetic conditions in which chain termination is governed by a bimolecular process. However, these models have been reported to disagree with experimental results. In a limiting case of nonideal kinetics it is assumed that primary termination is dominant. In this case the NPDD model must be modified to incorporate a quadratic relationship between the monomer concentration and the polymerization rate. By use of a multiharmonic expansion method of solution the predictions of ideal (bimolecular or linear) and nonideal (primary or quadratic) kinetic models are compared. By using these models we carried out numerical fits to experimental growth curves of gratings recorded in an acrylamide-based cross-linked photopolymer system. Superior fits are achieved by use of the primary termination model. Physical parameters such as the diffusion constant are extracted and compared with results previously reported in the literature.

Comparison of holographic photopolymer materials by use of analytic nonlocal diffusion models: errata

Comparison of holographic photopolymer materials by use of analytic nonlocal diffusion models: errata

Holographic edge-illuminated polymer Bragg gratings for dense wavelength division optical filters at 1550 nm.

We discuss the use of holographic photopolymer materials for use as dense wavelength division multiplexing filters in the C-band of the optical communication spectrum. An edge-illuminated hologram configuration is described that effectively extends the grating length to achieve narrow band filters operating near 1550 nm in photopolymers that are 100-200-microm thick. This configuration enables the formation of apodized and cascaded filter systems. Rouard's method is used to examine the properties of both apodization and cascaded gratings and indicates the potential for narrow spectral bandwidths (< 0.2 nm) and high side-lobe suppression (<-- 30 dB). Initial experimental results with a commercially available photopolymer are provided that verify narrowband spectral-transmittance properties (< 0.6 nm) and the ability to apodize the index profile. The primary limitation of the design is the absorption of existing photopolymer materials. Optimizing the polymer chemistry for filter design at 1550 nm may solve this problem.

Comparison of holographic photopolymer materials by use of analytic nonlocal diffusion models.

The one-dimensional diffusion equation governing holographic grating formation in photopolymers, which includes both nonlocal material response and generalized dependence of the rate of polymerization on the illuminating intensity, has been previously solved under the two-harmonic expansion assumption. The resulting analytic expressions for the monomer and polymer concentrations have been derived and their ranges of validity tested in comparison with the more accurate numerical four-harmonic case. We used these analytic expressions to carry out a study of experimental results presented in the literature over a 30-year period. Automatic fitting of the data with these formulas allows material parameters, including the nonlocal chain-length variance sigma, to be estimated. In this way, (i) a quantitative comparison of different materials can be made, and (ii) a standard form of experimental result presentation is proposed to facilitate such a procedure.

Reversible dye-doped holographic photopolymer materials for reconfigurable optical data storage

New self-developing reversible dye-doped holographic photopolymer materials were recently developed in our laboratory, which are sensitive to light from the green to near infrared wavelengths (500–850 nm) [1]. Previously, we have used liquid crystals in similar polymer matrices to increase the refractive index modulation [2]. In this work, we show that a new functionality of optical reconfiguration may be introduced if a reversible photosensitive dye is doped in the material. The compound we have used in this experiment is a multifunctional acrylic-based photopolymerizable material. Reversible dye and organic compound are added to serve as solvent and refractive index increasing agents. In addition, this dye may partially replace the liquid crystal’s role. Holographic recording characteristics of these materials were investigated. We have demonstrated that, the diffraction efficiency of recorded holograms and material sensitivity are high. We believe that these materials are very promising for applications in permanent, but reconfigurable diffractive optical elements.

Photopolymer-based stratified volume holographic optical elements

We report the implementation of stratified volume holographic optical elements (SVHOE's) using DuPont's Omnidex holographic photopolymer material and an in situ exposure technique for simultaneous multilayer grating recording. Experimental measurement of the +1-order angular sensitivity of a seven-layer SVHOE structure shows remarkable agreement with both theory and numerical simulation for incidence angles near the Bragg angle. For SVHOE's having modulation layers that individually operate in the Bragg or transition diffraction regimes, the envelope of the SVHOE angular sensitivity is experimentally shown to approximate closely that of a single modulation layer.

Photopolymer Material for Holography

An experimental Du Pont holographic photopolymer material produces an index modulation in excess of 10(-2) utilizing a diffusion mechanism. Optimum exposure in air is typically 30 mJ/cm(2) , in nitrogen 3 mJ/cm(2). Composition, beam ratio, and exposure power all affect the index modulation. This, combined with thickness variations, permits diffraction efficiency to be preadjusted for a variety of desired angular responses and spatial frequencies. The material can be easily overmodulated according to Kogelnik's phase grating theory. No wet processing is required. After total polymerization, storage at 100 degrees C, -60 degrees C, and under water does not significantly affect the diffraction efficiency. Image-object superposition is exact for real-time holography. Excellent copies of silver halide holograms with four times the original efficiency have been made. Grating devices with tailored peak or flat wavelength response can be constructed.

Photopolymer Material for Holography

An experimental Du Pont holographic photopolymer material produces an index modulation in excess of 10−2 utilizing a diffusion mechanism. Optimum exposure in air is typically 30 mJ/cm2, in nitrogen 3 mJ/cm2. Composition, beam ratio, and exposure power all affect the index modulation. This, combined with thickness variations, permits diffraction efficiency to be preadjusted for a variety of desired angular responses and spatial frequencies. The material can be easily overmodulated according to Kogelnik’s phase grating theory. No wet processing is required. After total polymerization, storage at 100°C, −60°C, and under water does not significantly affect the diffraction efficiency. Image–object superposition is exact for real-time holography. Excellent copies of silver halide holograms with four times the original efficiency have been made. Grating devices with tailored peak or flat wavelength response can be constructed.