Photopolymer Material Research Articles

Beam self-cleanup by use of self-written waveguide generated by photopolymerization.

A novel method for multimode fiber (MMF) laser-beam cleanup is introduced based on the optically induced growth and interaction of self-written waveguides (SWWs) in a photopolymer material. Theoretically, it is predicted that when the light is introduced into a free-radical photopolymerizable system from a MMF, the incident multichannel and structured beam shape can be caused to merge to form a single-channel Gaussian-like beam under specific exposure and material conditions. Experimental validation was carried out using a dry acrylamide/polyvinyl alcohol (AA/PVA) photopolymer sample. This work opens the door to studies involving self-developing laser beam cleanup and also to possible applications in photonic telecommunication systems and integrated optical devices.

Development of realistic physical breast phantoms matched to virtual breast phantoms based on human subject data.

Physical phantoms are essential for the development, optimization, and evaluation of x-ray breast imaging systems. Recognizing the major effect of anatomy on image quality and clinical performance, such phantoms should ideally reflect the three-dimensional structure of the human breast. Currently, there is no commercially available three-dimensional physical breast phantom that is anthropomorphic. The authors present the development of a new suite of physical breast phantoms based on human data. The phantoms were designed to match the extended cardiac-torso virtual breast phantoms that were based on dedicated breast computed tomography images of human subjects. The phantoms were fabricated by high-resolution multimaterial additive manufacturing (3D printing) technology. The glandular equivalency of the photopolymer materials was measured relative to breast tissue-equivalent plastic materials. Based on the current state-of-the-art in the technology and available materials, two variations were fabricated. The first was a dual-material phantom, the Doublet. Fibroglandular tissue and skin were represented by the most radiographically dense material available; adipose tissue was represented by the least radiographically dense material. The second variation, the Singlet, was fabricated with a single material to represent fibroglandular tissue and skin. It was subsequently filled with adipose-equivalent materials including oil, beeswax, and permanent urethane-based polymer. Simulated microcalcification clusters were further included in the phantoms via crushed eggshells. The phantoms were imaged and characterized visually and quantitatively. The mammographic projections and tomosynthesis reconstructed images of the fabricated phantoms yielded realistic breast background. The mammograms of the phantoms demonstrated close correlation with simulated mammographic projection images of the corresponding virtual phantoms. Furthermore, power-law descriptions of the phantom images were in general agreement with real human images. The Singlet approach offered more realistic contrast as compared to the Doublet approach, but at the expense of air bubbles and air pockets that formed during the filling process. The presented physical breast phantoms and their matching virtual breast phantoms offer realistic breast anatomy, patient variability, and ease of use, making them a potential candidate for performing both system quality control testing and virtual clinical trials.

Modeling the nonlinear photoabsorptive behavior during self-written waveguide formation in a photopolymer

Photopolymer materials can be used as recording media for self-written waveguides (SWWs) as they can exhibit a large refractive index change and high photo-sensitivity. In free radical photo-polymerization systems, the dyes, functioning as the photosensitizer, strongly influence the material properties. During photo-illumination the spatial and temporal evolution of the dye concentration is an important factor leading to nonlinear absorption. In this paper, based on an investigation of the photochemical mechanisms, we analyze the nonlinear photo-absorptive effect during the photo-initiation processes. The time varying exposing light distribution is calculated and used to iteratively estimate the evolving cross-sectional refractive index and loss coefficient values. The model enables a more accurate and physical description of the optically induced growth of SWWs in such systems. Then SWWs formed in dry acrylamide/polyvinyl alcohol (AA/PVA) based photopolymer samples, containing different initial dye concentrations, are experimentally examined. The nonlinear absorptive behavior is quantified by comparing the model predictions and the experimental results.

Characterization and comparison of different photopolymers for low spatial frequency recording

Free-radical photopolymer materials can be fabricated using a wide range of monomers, binders, dyes, etc. It was shown that in some photopolymers the surface and the internal diffusion for acrylamide materials are very different and also it was demonstrated the viability of acrylamide materials to achieve 2π phase depth for low spatial diffractive optical elements. Building on the work developed previously, in this paper, a characterization and a comparison is carried out for three different photopolymers: crosslinked acrylamide based photopolymers, a biophotopol and an H-PDLC material. We have measured the motion of the components inside the material and through the surface using a new index matching component and through the surface. We have studied the introduction of different crosslinkers in order to increase the refractive index modulation and to reduce the thickness required to achieve a phase depth higher than 2π in the diffraction optical elements.

Hydrophobic photopolymerizable nanostructured hybrid materials: An effective solution for the protection of porous stones

In order to guarantee a very high preservation of stone artworks from water actions, an experimental superhydrophobic photopolymerizable organic–inorganic (O‐I) nanostructured hybrid product, namely HEP, has been developed and tested on a calcarenitic stone characteristic of Apulia Region (Italy), i.e., Pietra Leccese (PL). HEP is a “green” product, not containing harmful solvents, and is able to quickly set and harden at room temperature. The first part of the work was devoted to the analysis of the dimension of the silica nanodomains and the suitability of the liquid system produced to be applied on stone surfaces. To this aim, dynamic light scattering and rheological analyses were performed after different times from the preparation of the O‐I system. The hybrid mixture was subsequently applied on a glass substrate and photopolymerized by UV lamp. Several physical properties (glass transition temperature, transparency, scratch, and surface hardness) were, then, measured on the hybrid coating: a substantial improvement of all the surface properties measured was observed. HEP was, finally, applied on PL elements and different analytical techniques (contact angle, colorimetric and water absorption measurements, liquid water, and vapor water transmission) were used to fully characterize the product in terms of hydrophobicity, protective efficacy, water penetration resistance, and transpiring capability. The protective properties of the novel hybrid coating were also compared with those of two commercial water‐repellent products, applied on the same stone substrate, evidencing that the experimental coating is able to equal the performance of high‐quality commercial products. POLYM. COMPOS., 36:1039–1047, 2015. © 2015 Society of Plastics Engineers

Development of Periodic and Three-Dimensional Structures in Acrylic-Monomer Photopolymer Materials by Holographic Methods

We show the possibility and advantages of using photopolymer materials based on acrylic monomers and nanocomposites in holography. Holographic characteristics of these materials and conditions for forming periodic structures and three-dimensional elements in them are determined.

Self-written waveguides in a dry acrylamide/polyvinyl alcohol photopolymer material.

For the first time it is demonstrated that permanent optical waveguides can be self-written in a solid acrylamide/polyvinyl alcohol photopolymer material. The novel (to our knowledge) technique used to prepare the polymeric medium used is described. It is demonstrated that the resulting waveguides formed can be used to guide different wavelengths. A standard theoretical model is used to predict both the evolution of the light intensity distribution and the channel formation inside the material during the exposure. The experimental results and the numerical simulations are compared, and good agreement is obtained.

PQ/PMMA photopolymer: Modelling post-exposure

Phenanthrenequinone (PQ) doped poly(methyl methacrylate) (PMMA) photopolymer material is currently being actively investigated. A previously developed 1-D Nonlocal Photo-polymerization Driven Diffusion (NPDD) model is applied to further examine the behavior of the material post-exposure. The use of the nonlocal parameter when examining PQ/PMMA is discussed. The resulting predicted evolution of the first harmonic refractive index modulation is simulated both: (i) a long time post-exposure, and (ii) in the case of thermal treatment post-exposure. The convergence of the numerical simulations is examined, when both 12 and 4 spatial concentration harmonics are retained in the Fourier series expansions describing the various component material distributions. Several physical processes are studied, including the nonlocal material response and the effects of the diffusion of both the ground state and excited states PQ molecules (during and post-exposure). The effects of the use of different exposing intensities on the final grating formed are studied. The size of the higher grating harmonic concentration amplitudes in this final distribution is also discussed. Thus in this paper for the first time the effects/treatments taking place post-exposure are systematically studied. Our aim is to characterize the final stable grating. We show that both the nonlocal effect and the diffusion of the PQ excited states tend to weaken the PQ-PMMA grating but lead to higher fidelity of the recorded pattern. It is also shown that higher harmonic gratings are generated when higher exposing intensity is applied.

Analysis of the absorptive behavior of photopolymer materials. Part II. Experimental validation

In the first part of this paper, a model describing photopolymer materials, which incorporates both the physical electromagnetic and photochemical effects taking place, was developed. This model is now validated by applying it to fit experimental data for two different types of photopolymer materials. The first photopolymer material, acrylamide/polyvinyl alcohol, is studied when four photosensitizers are used, i.e. Erythrosine B, Eosin Y, Phloxine B and Rose Bengal. The second type of photopolymer material involves phenanthrenequinone in a polymethylmethacrylate matrix. Using our model, the values of physical parameters, are extracted by numerical fitting experimentally obtained normalized transmittance growth curves. Experimental data sets for different exposure intensities, dye concentrations, and exposure geometries are studied. The advantages of our approach are demonstrated and it is shown that the parameters proposed by us to quantify the absorptive behavior in our model are both physical and can be estimated.

Three-dimensional extended nonlocal photopolymerization driven diffusion model Part I Absorption

When holographic gratings are recorded in a photopolymer material layer, the spatial distributions of the photoreactions taking place lead to the formation of nonuniform gratings in depth. In an effort to study such effects, in this series of papers a three-dimensional (3D) nonlocal photopolymerization driven diffusion (NPDD) model is developed. In Part I, we focused on describing the photoinitiation mechanisms by introducing a 3D dye absorption model that more accurately and physically describes the processes taking place. Then, the values of physical parameters are extracted by numerically fitting experimentally obtained normalized transmittance growth curves for a range of layer thicknesses in an acrylamide/polyvinyl alcohol (AA/PVA) photopolymer material sensitized by Erythrosine B (EB). In Part II [J. Opt. Soc. Am. B31, 2648 (2014)10.1364/JOSAB.31.002648JOBPDE0740-3224], applying the results in Part I, the full 3D photophysical and photochemical evolutions are modeled. Then the resulting 3D NPDD model is validated experimentally.

Three-dimensional extended nonlocal photopolymerization driven diffusion model Part II Photopolymerization and model development

In Part I of this paper [J. Opt. Soc. Am. B31, 2638 (201410.1364/JOSAB.31.002638JOBPDE0740-3224)], an absorption model is used to predict the dye concentration and light intensity distribution inside a photopolymer medium volume. These results are now used as inputs to a Runge–Kutta algorithm acting as a subgrid of the finite-difference time-domain (FDTD) method. In this way, a full 3D time-dependent nonlocal photopolymerization driven diffusion model is implemented. This enables a more accurate and physical description of the evolutions of the holographic grating. The validity of the proposed model is examined by applying it to fit experimental data for acrylamide/polyvinyl alcohol photopolymer material layers containing the photosensitizer erythrosine B. Material parameter values are estimated by numerically fitting the experimentally obtained refractive index modulation growth curves and angular scans.

Analysis of the absorptive behavior of photopolymer materials. Part I. Theoretical modeling

Photopolymers have received a great deal of attention due to their broad range of applications. The variation of their absorptive behavior during exposure is pivotal to the study of such materials. A model combining the associated electromagnetics and photochemical kinetics is presented to describe these absorptive processes. Such a model is critical in describing both self-modulations during holographic recording and also self-focusing effects. To describe the photophysical and photochemical changes taking place, a modulated equivalent electrical conductivity is introduced. Temporal variations of the concentrations of dye, monomer, and polymer are then predicted using the modified nonlocal photopolymerization driven diffusion model. The numerical convergence of the model is examined. Comparisons between the predictions of the model and experimental results, for both acrylamide/polyvinyl alcohol and Phenanthrenequinone doped poly(methyl methacrylate) photopolymer materials, are presented and analyzed in Part II of this paper.

Engineering topochemical polymerizations using block copolymer templates.

With the aim to achieve rapid and efficient topochemical polymerizations in the solid state, via solution-based processing of thin films, we report the integration of a diphenyldiacetylene monomer and a poly(styrene-b-acrylic acid) block copolymer template for the generation of supramolecular architectural photopolymerizable materials. This strategy takes advantage of non-covalent interactions to template a topochemical photopolymerization that yields a polydiphenyldiacetylene (PDPDA) derivative. In thin films, it was found that hierarchical self-assembly of the diacetylene monomers by microphase segregation of the block copolymer template enhances the topochemical photopolymerization, which is complete within a 20 s exposure to UV light. Moreover, UV-active cross-linkable groups were incorporated within the block copolymer template to create micropatterns of PDPDA by photolithography, in the same step as the polymerization reaction. The materials design and processing may find potential uses in the microfabrication of sensors and other important areas that benefit from solution-based processing of flexible conjugated materials.

On-chip near-infrared optical spectrometer based on single-mode Epo waveguide and gold nanoantennas

We report about optical spectrometry using gold nanostructures printed on top of an integrated optical waveguide. The optical waveguide is a single-mode buried waveguide made from a combination of photo-polymerizable materials and is fabricated by photolithography on a glass substrate. To detect the electric field inside the waveguide, a gold nanocoupler array of thin lines (50 nm thick and 8 μm in length) is embedded on top of the aforementioned waveguide. They are produced by e-beam lithography. Both waveguide ports are polished, and the output port, in particular, is coated with a thin gold layer to assimilate a mirror and hence, it enables the creation of stationary waves inside the structure. Stationary waves generated inside the guide constitute a spatial interferogram. Locally, light is out-coupled using the nanocouplers and allows measuring the interferogram structure. The resulting pattern is imaged by a vision system involving an optical microscope with the objective lenses of different magnifications and a digital camera mounted on top of the microscope. The 5× objective lens demonstrates a superior performance in retrieving the investigated spectrum compared to 20× and 100× objectives. Fast Fourier transform is performed on the captured signal to extract the spectral content of the measured signal.

Formation of the Printing Elements in the Photopolymer Material Used in Flexography

Starting point of this paper is photopolymer printing plate used for flexographic printing. It is used for transfer of the printing ink onto the printing surface during the reproduction process. Photopolymer printing plate consists of several layers: polyester basis, photo sensitive polymer material and LAMS - Laser Ablation Mask. In the platemaking process the photosensitive material, which will form a printing plate, has to be several time exposed to different radiation in order to obtain a functional printability performance. LAMS layer has a role of masking in the exposure process. Upon pre-exposure, LAMS layer has to be removed by laser ablation only at the surfaces where photopolymer printing plate needs to be exposed. After ablation the exposures to UV lights follows and the plate will be finished with chemical removal of the unexposed parts of the polymer. Functionality of the finished printing plate has to be characterised and monitored in every procedure step because the formed image element on the printing plate has a major influence on the quality of the finished printed product. In this paper observing of the changes in the polymer material which is caused by exposure through LAMS layer will be performed. The aim is to measure the surface openings on the LAMS mask and to measure surface coverage (image elements) on the polymer material formed by exposure through the LAMS. Measuring will be made by image analysis software based on microscopic images of the control fields of differing halftone values. It is assumed that there will be a correlation between the LAMS openings and formed image elements on the printing plates. Preliminary results indicate that certain differences in image elements can be detected and are probably the consequence of the different amount of irradiated surface of the polymer material. Since the polymer material which forms the printing plate should be stable in the graphic reproduction process, results of the paper will explain the influence of UV exposures on polymerisation process and on the functional printability performance of the plates.

Optical compensation for hologram distortion using wavefront interpolation in angle-multiplexed holograms

Distortion of the hologram may occur when the photopolymer material used in the medium shrinks or expands. We analyzed interference fringe distortion for plane waves and a reference beam with an angular gap between recording and reproducing for the purpose of compensating for the distortion. We found that the wavefronts that could compensate for the distortion could approximately be obtained by linear interpolation of such angle-multiplexed holograms. We recorded 80 data pages with the angle-multiplexing method and obtained an optimized wavefront to compensate for hologram distortion on the first, fortieth, and eightieth data pages using adaptive optics with genetic algorithms and linear interpolated wavefronts at the other data pages. The calculation time for 80 wavefronts to compensate for distortion fell to 3/80th of that of having to calculate optimizations for all pages. The bit error rates were lower than 1.0 × 10−2 on all data pages reproduced using these wavefronts.

Biomimetic superoxide dismutase stabilized by photopolymerization for superoxide anions biosensing and cell monitoring.

Photopolymerization strategy, as one of the immobilization methods, has attracted considerable interest because of some advantages, such as easy operation, harmlessness to the biomolecules, and long storage stability. (E)-4-(4-Formylstyryl) pyridine (formylstyrylpyridine) was prepared through Heck reaction and used as a photopolymer material to immobilize biomimetic superoxide dismutase under ultraviolet irradiation (UV) irradiation in a short time. The styrylpyridinium moiety of Formylstyrylpyridine was photoreactive and formed a dimer under UV irradiation. Mn2P2O7 multilayer sheet, a novel superoxide dismutase mimic, was synthesized. The formed photopolymer can immobilize Mn2P2O7 firmly under UV irradiation. On the basis of high catalytic activity of Mn2P2O7 biomimetic enzyme and long-term stability of Mn2P2O7-formylstyrylpyridine film, after introducing multiwalled carbon nanotubes (MWCNTs), a novel electrochemical biosensing platform called MWCNTs/Mn2P2O7-formylstyrylpyridine for superoxide anion (O2(•-)) detection was constructed. The biosensor displayed good performance for O2(•-) detection and provided a reliable platform to adhere living cells directly on the modified electrode surface. Therefore, the biosensor was successfully applied to vitro determination of O2(•-) released from living cells, which had a promising prospect for living cells monitoring and diagnosis of reactive oxygen species-related diseases.

Técnica simplificada en la rehabilitación del desdentado

In this paper we present a simplified rehabilitation technique for the edentulous through removable prosthesis that achieve the goal of the treatment in only three clinical appointments. This accomplishment is possible through the use of a photopolymerizable material, performing an impression tray directly in the mouth without making any preliminary models; it thereby enables to take preliminary and definitive impressions, and intermaxillary relations in a single session. Rev. Clin. Periodoncia Implantol. Rehabil. Oral Vol. 7(1); 17-20, 2014.

Using acrylamide-based photopolymers for fabrication of holographic optical elements in solar energy applications

A holographic device is under development that aims to improve light collection in solar cells. The aim is to explore the potential of using photopolymer holographic optical elements (HOEs) to collect light from a moving source, such as the sun, and redirect it for concentration by a holographic lens. A working range of 45° is targeted for such a device to be useful in solar applications without tracking. A photopolymer HOE is capable of efficiently redirecting light, but the angular selectivity of a single grating is usually of the order of one degree at the thicknesses required for high efficiency. The challenge here is to increase the angular and wavelength range of the gratings so that a reasonable number may be multiplexed and/or combined to create a device that can concentrate light incident from a large range of angles. In this paper, low spatial frequency holographic recording is explored to increase the angular and wavelength range of an individual grating. Ultimately, a combination of gratings will be used so that a broad range of angles of incidence are accepted. A design is proposed for the combination of such elements into a holographic solar collector. The first step in achieving this is optimization of recording at low spatial frequency. This requires a photopolymer material with unique properties, such as a fast monomer diffusion rate. This paper reports results on the efficiency of holograms recorded in an acrylamide-based photopolymer at low spatial frequencies (100, 200, and 300 l/mm). The diffraction efficiency and angular selectivity of recorded holograms have been studied for various photopolymer layer thicknesses and different intensities of the recording beams. A diffraction efficiency of over 80% was achieved at a spatial frequency of 200 l/mm. The optimum intensity of recording at this spatial frequency was found to be 1 mW/cm2. Individual gratings and focusing elements with high efficiency and FWHM angles of 3° are experimentally demonstrated.

Comparison of a new photosensitizer with erythrosine B in an AA/PVA-based photopolymer material

Dyes often act as the photoinitiator PI/photosensitizer PS in photopolymer materials and are therefore of significant interest. The properties of the PI/PS used strongly influences grating formation when the material layer is exposed holographically. In this paper, the ability of a recently synthesized dye, D_1, to sensitize an acrylamide/polyvinyl alcohol (AA/PVA) based photopolymer is examined, and the material performance is characterized using an extended nonlocal photopolymerization-driven diffusion model. Electron spin resonance spin-trapping (ESR-ST) experiments are also carried out to characterize the generation of the initiator/primary radical, R(•), during exposure. The results obtained are then compared with those for the corresponding situation when using a xanthene dye, i.e., erythrosine B, under the same experiment conditions. The results indicate that the nonlocal effect is greater when this new photosensitizer is used in the material. Analysis indicates that this is the case because of the dye's (D_1) weak absorptivity and the resulting slow rate of primary radical production.