The Experts below are selected from a list of 5082 Experts worldwide ranked by ideXlab platform
Inmaculada Pascual - One of the best experts on this subject based on the ideXlab platform.
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LED-Cured Reflection Gratings Stored in an Acrylate-Based Photopolymer
'MDPI AG', 2019Co-Authors: Manuel G. Ramírez, Manuel Ortuno, Jorge Frances, Daniel Sirvent, Marta Morales-vidal, Francisco J. Martínez-guardiola, Inmaculada PascualAbstract:The storage of volume holographic reflection gratings in low-toxicity Photopolymers represents a challenge at present since they can be used in many important applications such as biosensors and holographic optical elements. In this context, an acrylate-based Photopolymer developed in our research group was employed to study the recording of unslanted holographic reflection gratings at high spatial frequencies. The optimal preparation conditions of the Photopolymer layers were determinated. The diffraction efficiencies are measured in both recording and curing stage and a comparative study of these values was realized. In addition, a theoretical study using Kogelnik’s coupled wave theory was carried out with the aim of understanding the diffraction efficiency behaviour of both processes. In this work, a maximum diffraction efficiency of 14.1% was reached after a curing process in 150 µm layers at a recording wavelength of 488 nm. This value represents a good result compared to that reported in the literature and opens the way to reflection mode holography research using low-toxicity material
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characterization and comparison of different Photopolymers for low spatial frequency recording
Optical Materials, 2015Co-Authors: Roberto Fernandez, Sergi Gallego, Jorge Frances, Inmaculada Pascual, Augusto BeléndezAbstract:Abstract 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 2 π 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 2 π in the diffraction optical elements.
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model of low spatial frequency diffractive elements recorded in Photopolymers during and after recording
Optical Materials, 2014Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Jorge Frances, Cristian Neipp, Inmaculada Pascual, Roberto Fernandez, Martinez J Guardiola, Augusto BeléndezAbstract:Abstract Photopolymer are appealing materials for diffractive elements recording. Two of their properties when they are illuminated are useful for this goal: the relief surface changes and the refractive index modifications. In this paper we use a 2-dimensional model, based on direct parameter measurements, for predicting the refractive index distributions during and after illumination. We have analyzed different recording spatial frequencies for Photopolymers based on PVA/Acrylamide. This model was successfully applied to different Photopolymer compositions with different values of monomer diffusion and polymerization rates.
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surface relief model for Photopolymers without cover plating
Optics Express, 2011Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Stephan Marini, Jorge Frances, Augusto Beléndez, Inmaculada PascualAbstract:Relief surface changes provide interesting possibilities for storing diffractive optical elements on Photopolymers and are an important source of information to characterize and understand the material behaviour. In this paper we present a 3-dimensional model based on direct measurements of parameters to predict the relief structures generated on the material. This model is successfully applied to different Photopolymers with different values of monomer diffusion. The importance of monomer diffusion in depth is also discussed.
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spatial phase modulation based study of polyvinyl alcohol acrylamide Photopolymers in the low spatial frequency range
Applied Optics, 2009Co-Authors: Sergi Gallego, Stephan Marini, Augusto Beléndez, David Gil Mendez, Andre Marquez, Inmaculada PascualAbstract:Photopolymers are appealing materials for the fabrication of diffractive optical elements (DOEs). We evaluate the possibilities of polyvinyl-alcohol/acrylamide-based Photopolymers to store diffractive elements with low spatial frequencies. We record gratings with different spatial frequencies in the material and analyze the material behavior measuring the transmitted and the reflected orders as a function of exposition. We study two different compositions for the Photopolymer, with and without a cross-linker. The values of diffraction efficiency achieved for both compositions make the material suitable to record DOEs with long spatial periods. Assuming a Fermi-Dirac-function-based profile, we fitted the diffracted intensities (up to the eighth order) to obtain the phase profile of the recorded gratings. This analysis shows that it is possible to achieve a phase shift larger than 2π rad with steep edges in the periodic phase profile. In the case of the measurements in reflection, we have obtained information dealing with the surface profile, which show that it has a smooth shape with an extremely large phase-modulation depth.
John T Sheridan - One of the best experts on this subject based on the ideXlab platform.
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non local photo polymerization kinetics including multiple termination mechanisms and dark reactions part iii primary radical generation and inhibition
Journal of The Optical Society of America B-optical Physics, 2010Co-Authors: Michael R Gleeson, Jinxin Guo, Shui Liu, John T SheridanAbstract:Photopolymers are playing an ever more important role in diverse areas of research such as holographic data storage, hybrid photonic circuits, and solitary waves. In each of these applications, the production of primary radicals is the driving force of the polymerization processes. Therefore an understanding of the production, removal, and scavenging processes of free radicals in a Photopolymer system is crucial in determining a material’s response to a given exposure. One such scavenging process is inhibition. In this paper the non-local photo-polymerization driven diffusion model is extended to more accurately model the effects of (i) time varying primary radical production, (ii) the rate of removal of photosensitizer, and (iii) inhibition. The model is presented to specifically analyze the effects of inhibition, which occur most predominantly at the start of grating growth, and comparisons between theory and experiment are performed which quantify these effects.
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nonlocal Photopolymerization kinetics including multiple termination mechanisms and dark reactions part ii experimental validation
Journal of The Optical Society of America B-optical Physics, 2009Co-Authors: Michael R Gleeson, Shui Liu, Robert R Mcleod, John T SheridanAbstract:In the first of this series of papers [J. Opt. Soc. Am. B26, 1736 (2009)], a new kinetic model, which includes most of the major photochemical and nonlocal Photopolymerization driven diffusion effects, was proposed. Predictions made using the model were presented, and the numerical convergence of these simulations were examined when retaining higher-concentration harmonics. The validity and generality of the model is examined by applying it to fit experimental data for two different types of Photopolymer material appearing in the literature. The first of these Photopolymer materials involves an acrylamide monomer in a polyvinylalcohol matrix. The second is a more complex Photopolymer in an epoxy resin matrix. Using the new model, key material parameters are extracted by numerically fitting experimentally obtained diffraction efficiency growth curves. The growth curves used include data captured both during exposure and post-exposure, allowing examination and analysis of “dark reactions.”
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physical and effective optical thickness of holographic diffraction gratings recorded in Photopolymers
Optics Express, 2005Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Cristian Neipp, Augusto Beléndez, Inmaculada Pascual, John V Kelly, John T SheridanAbstract:In recent years the interest in thick holographic recording materials for storage applications has increased. In particular, Photopolymers are interesting materials for obtaining inexpensive thick dry layers with low noise and high diffraction efficiencies. Nonetheless, as will be demonstrated in this work, the attenuation in depth of light during the recording limits dramatically the effective optical thickness of the material. This effect must be taken into account whenever thick diffraction gratings are recorded in Photopolymer materials. In this work the differences between optical and physical thickness are analyzed, applying a method based on the Rigorous Coupled Wave Theory and taking into account the attenuation in depth of the refractive index profile. By doing this the maximum optical thickness that can be achieved can be calculated. When the effective thickness is known, then the real storage capacity of the material can be obtained.
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nonlocal polymerization driven diffusion model based examination of the scaling law for holographic data storage
Optics Letters, 2005Co-Authors: John T Sheridan, Michael Gleeson, John V Kelly, Feidhlim T OneillAbstract:For the first time to our knowledge, a detailed theoretical basis is provided for the well-known inverse-square scaling law of holographic diffraction, which states that replay diffraction efficiency ?=?/M2, where M is the number of gratings stored and ? is a constant system parameter. This law is shown to hold for Photopolymer recording media governed by the predictions of the nonlocal polymerization-driven diffusion model. On the basis of the analysis, we (i) propose a media inverse scaling law, (ii) relate ? to Photopolymer material parameters and the hologram geometry and replay conditions, and (iii) comment on the form and validity of the diffraction efficiency inverse-square scaling law for higher-diffraction-efficiency gratings.
Sergi Gallego - One of the best experts on this subject based on the ideXlab platform.
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Tunable Waveguides Couplers Based on HPDLC for See-Through Applications
'MDPI AG', 2021Co-Authors: Sergi Gallego, Manuel Ortuno, Manuel G. Ramírez, Marta Morales-vidal, Daniel Puerto, Soumia I. Taleb, Antonio Hernández, Cristian NeippAbstract:Photopolymers have become an important recording material for many applications, mainly related to holography. Their flexibility to change the chemical composition together with the optical properties made them a versatile holographic recording material. The introduction of liquid crystal molecules in a Photopolymer based on multifunctional monomer provides us the possibility to generate tunable holograms. The switchable holographic elements are a key point for see-through applications. In this work, we optimize the holographic polymer-dispersed liquid crystals composition to improve the performance of tunable waveguide couplers based on transmission gratings and specifically their response under an applied electric field. A variation around 60% in the transmission efficiency was achieved
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characterization and comparison of different Photopolymers for low spatial frequency recording
Optical Materials, 2015Co-Authors: Roberto Fernandez, Sergi Gallego, Jorge Frances, Inmaculada Pascual, Augusto BeléndezAbstract:Abstract 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 2 π 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 2 π in the diffraction optical elements.
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model of low spatial frequency diffractive elements recorded in Photopolymers during and after recording
Optical Materials, 2014Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Jorge Frances, Cristian Neipp, Inmaculada Pascual, Roberto Fernandez, Martinez J Guardiola, Augusto BeléndezAbstract:Abstract Photopolymer are appealing materials for diffractive elements recording. Two of their properties when they are illuminated are useful for this goal: the relief surface changes and the refractive index modifications. In this paper we use a 2-dimensional model, based on direct parameter measurements, for predicting the refractive index distributions during and after illumination. We have analyzed different recording spatial frequencies for Photopolymers based on PVA/Acrylamide. This model was successfully applied to different Photopolymer compositions with different values of monomer diffusion and polymerization rates.
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surface relief model for Photopolymers without cover plating
Optics Express, 2011Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Stephan Marini, Jorge Frances, Augusto Beléndez, Inmaculada PascualAbstract:Relief surface changes provide interesting possibilities for storing diffractive optical elements on Photopolymers and are an important source of information to characterize and understand the material behaviour. In this paper we present a 3-dimensional model based on direct measurements of parameters to predict the relief structures generated on the material. This model is successfully applied to different Photopolymers with different values of monomer diffusion. The importance of monomer diffusion in depth is also discussed.
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high environmental compatibility Photopolymers compared to pva aa based materials at zero spatial frequency limit
Optical Materials, 2011Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Stephan Marini, Jorge FrancesAbstract:Abstract In holographic applications the direct parameters determination of Photopolymers as optical recording media is a very difficult task due to the presence of two different phenomena: polymer formation and monomer diffusion. We propose a direct method based on zero spatial frequency recording, to eliminate the diffusion influence, and on interferometric techniques, both in transmission and in reflection, to obtain quantitative values of: shrinkage, polymerization rate, polymer refractive index and relation between polymerization and recording intensity. Recent investigations confirm the toxic potential of acrylamide. Starting from polyvinylalcohol/acrylamide Photopolymer we have proposed different compositions of new competitive Photopolymers with high environmental compatibility. We have studied the ways to optimize the optical behavior and the environmental compatibility. Parameters comparison with the polyvinylalcohol/acrylamide Photopolymers shows significant differences.
Augusto Beléndez - One of the best experts on this subject based on the ideXlab platform.
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characterization and comparison of different Photopolymers for low spatial frequency recording
Optical Materials, 2015Co-Authors: Roberto Fernandez, Sergi Gallego, Jorge Frances, Inmaculada Pascual, Augusto BeléndezAbstract:Abstract 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 2 π 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 2 π in the diffraction optical elements.
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model of low spatial frequency diffractive elements recorded in Photopolymers during and after recording
Optical Materials, 2014Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Jorge Frances, Cristian Neipp, Inmaculada Pascual, Roberto Fernandez, Martinez J Guardiola, Augusto BeléndezAbstract:Abstract Photopolymer are appealing materials for diffractive elements recording. Two of their properties when they are illuminated are useful for this goal: the relief surface changes and the refractive index modifications. In this paper we use a 2-dimensional model, based on direct parameter measurements, for predicting the refractive index distributions during and after illumination. We have analyzed different recording spatial frequencies for Photopolymers based on PVA/Acrylamide. This model was successfully applied to different Photopolymer compositions with different values of monomer diffusion and polymerization rates.
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surface relief model for Photopolymers without cover plating
Optics Express, 2011Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Stephan Marini, Jorge Frances, Augusto Beléndez, Inmaculada PascualAbstract:Relief surface changes provide interesting possibilities for storing diffractive optical elements on Photopolymers and are an important source of information to characterize and understand the material behaviour. In this paper we present a 3-dimensional model based on direct measurements of parameters to predict the relief structures generated on the material. This model is successfully applied to different Photopolymers with different values of monomer diffusion. The importance of monomer diffusion in depth is also discussed.
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spatial phase modulation based study of polyvinyl alcohol acrylamide Photopolymers in the low spatial frequency range
Applied Optics, 2009Co-Authors: Sergi Gallego, Stephan Marini, Augusto Beléndez, David Gil Mendez, Andre Marquez, Inmaculada PascualAbstract:Photopolymers are appealing materials for the fabrication of diffractive optical elements (DOEs). We evaluate the possibilities of polyvinyl-alcohol/acrylamide-based Photopolymers to store diffractive elements with low spatial frequencies. We record gratings with different spatial frequencies in the material and analyze the material behavior measuring the transmitted and the reflected orders as a function of exposition. We study two different compositions for the Photopolymer, with and without a cross-linker. The values of diffraction efficiency achieved for both compositions make the material suitable to record DOEs with long spatial periods. Assuming a Fermi-Dirac-function-based profile, we fitted the diffracted intensities (up to the eighth order) to obtain the phase profile of the recorded gratings. This analysis shows that it is possible to achieve a phase shift larger than 2π rad with steep edges in the periodic phase profile. In the case of the measurements in reflection, we have obtained information dealing with the surface profile, which show that it has a smooth shape with an extremely large phase-modulation depth.
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analysis of pva aa based Photopolymers at the zero spatial frequency limit using interferometric methods
Applied Optics, 2008Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Cristian Neipp, Inmaculada Pascual, David Gil Mendez, Elena Fernandez, Augusto BeléndezAbstract:One of the problems associated with Photopolymers as optical recording media is the thickness variation during the recording process. Different values of shrinkages or swelling are reported in the literature for Photopolymers. Furthermore, these variations depend on the spatial frequencies of the gratings stored in the materials. Thickness variations can be measured using different methods: studying the deviation from the Bragg's angle for nonslanted gratings, using MicroXAM S/N 8038 interferometer, or by the thermomechanical analysis experiments. In a previous paper, we began the characterization of the properties of a polyvinyl alcohol/acrylamide based Photopolymer at the lowest end of recorded spatial frequencies. In this work, we continue analyzing the thickness variations of these materials using a reflection interferometer. With this technique we are able to obtain the variations of the layers refractive index and, therefore, a direct estimation of the polymer refractive index.
Jorge Frances - One of the best experts on this subject based on the ideXlab platform.
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LED-Cured Reflection Gratings Stored in an Acrylate-Based Photopolymer
'MDPI AG', 2019Co-Authors: Manuel G. Ramírez, Manuel Ortuno, Jorge Frances, Daniel Sirvent, Marta Morales-vidal, Francisco J. Martínez-guardiola, Inmaculada PascualAbstract:The storage of volume holographic reflection gratings in low-toxicity Photopolymers represents a challenge at present since they can be used in many important applications such as biosensors and holographic optical elements. In this context, an acrylate-based Photopolymer developed in our research group was employed to study the recording of unslanted holographic reflection gratings at high spatial frequencies. The optimal preparation conditions of the Photopolymer layers were determinated. The diffraction efficiencies are measured in both recording and curing stage and a comparative study of these values was realized. In addition, a theoretical study using Kogelnik’s coupled wave theory was carried out with the aim of understanding the diffraction efficiency behaviour of both processes. In this work, a maximum diffraction efficiency of 14.1% was reached after a curing process in 150 µm layers at a recording wavelength of 488 nm. This value represents a good result compared to that reported in the literature and opens the way to reflection mode holography research using low-toxicity material
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characterization and comparison of different Photopolymers for low spatial frequency recording
Optical Materials, 2015Co-Authors: Roberto Fernandez, Sergi Gallego, Jorge Frances, Inmaculada Pascual, Augusto BeléndezAbstract:Abstract 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 2 π 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 2 π in the diffraction optical elements.
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model of low spatial frequency diffractive elements recorded in Photopolymers during and after recording
Optical Materials, 2014Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Jorge Frances, Cristian Neipp, Inmaculada Pascual, Roberto Fernandez, Martinez J Guardiola, Augusto BeléndezAbstract:Abstract Photopolymer are appealing materials for diffractive elements recording. Two of their properties when they are illuminated are useful for this goal: the relief surface changes and the refractive index modifications. In this paper we use a 2-dimensional model, based on direct parameter measurements, for predicting the refractive index distributions during and after illumination. We have analyzed different recording spatial frequencies for Photopolymers based on PVA/Acrylamide. This model was successfully applied to different Photopolymer compositions with different values of monomer diffusion and polymerization rates.
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surface relief model for Photopolymers without cover plating
Optics Express, 2011Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Stephan Marini, Jorge Frances, Augusto Beléndez, Inmaculada PascualAbstract:Relief surface changes provide interesting possibilities for storing diffractive optical elements on Photopolymers and are an important source of information to characterize and understand the material behaviour. In this paper we present a 3-dimensional model based on direct measurements of parameters to predict the relief structures generated on the material. This model is successfully applied to different Photopolymers with different values of monomer diffusion. The importance of monomer diffusion in depth is also discussed.
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high environmental compatibility Photopolymers compared to pva aa based materials at zero spatial frequency limit
Optical Materials, 2011Co-Authors: Sergi Gallego, Andres Marquez, Manuel Ortuno, Stephan Marini, Jorge FrancesAbstract:Abstract In holographic applications the direct parameters determination of Photopolymers as optical recording media is a very difficult task due to the presence of two different phenomena: polymer formation and monomer diffusion. We propose a direct method based on zero spatial frequency recording, to eliminate the diffusion influence, and on interferometric techniques, both in transmission and in reflection, to obtain quantitative values of: shrinkage, polymerization rate, polymer refractive index and relation between polymerization and recording intensity. Recent investigations confirm the toxic potential of acrylamide. Starting from polyvinylalcohol/acrylamide Photopolymer we have proposed different compositions of new competitive Photopolymers with high environmental compatibility. We have studied the ways to optimize the optical behavior and the environmental compatibility. Parameters comparison with the polyvinylalcohol/acrylamide Photopolymers shows significant differences.