Ms. Ciara E. Close Profile

Ciara E. Close

Student at Univ College Dublin

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Author

Publications (21)

Proceedings Article | 15 May 2010 Paper

Using short exposures to approximate diffusion rates

C. Close, M. Gleeson, J. Sheridan

Proceedings Volume 7717, 77171O (2010) https://doi.org/10.1117/12.854985

KEYWORDS: Diffusion, Polymers, Diffraction gratings, Diffraction, Modulation, Refractive index, Holography, Polymerization, Holographic materials, Modeling

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Proceedings Article | 14 May 2010 Paper

Approximating monomer diffusion in the Raman-Nath regime

C. Close, M. Gleeson, J. Sheridan

Proceedings Volume 7717, 77170S (2010) https://doi.org/10.1117/12.854979

KEYWORDS: Diffusion, Diffraction gratings, Holography, Diffraction, Photopolymers, Volume holography, Refractive index, Modulation, Polymers, CCD cameras

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Proceedings Article | 25 April 2008 Paper

Improvement of photopolymer materials for holographic data storage

Michael Gleeson, Shui Liu, Ciara Close, Dusan Sabol, John Sheridan

Proceedings Volume 6994, 69940P (2008) https://doi.org/10.1117/12.781650

KEYWORDS: Diffusion, Refractive index, Polymers, Spatial frequencies, Modulation, Holography, Polymerization, Photopolymers, Oxygen, Data storage

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Proceedings Article | 27 September 2007 Paper

Photopolymer material used in the recording of slanted gratings

Dusan Sabol, Michael Gleeson, Ciara Close, Shui Liu, John Sheridan

Proceedings Volume 6698, 66981G (2007) https://doi.org/10.1117/12.736901

KEYWORDS: Diffraction gratings, Modulation, Holography, Absorption, Photopolymers, Molecules, Electromagnetism, Diffusion, Quantum efficiency, Diffraction

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Proceedings Article | 27 September 2007 Paper

Photopolymer materials for holographic data storage applications

John Sheridan, Michael Gleeson, Ciara Close, Dusan Sabol

Proceedings Volume 6698, 669807 (2007) https://doi.org/10.1117/12.739044

KEYWORDS: Data storage, Holography, Dysprosium, Diffusion, Polymers, Photopolymers, Polymerization, Molecules, Spatial frequencies, Holographic materials

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Proceedings Article | 13 September 2006 Paper

Impacts of modifier chemicals on the rates of diffusion in Acrylamide/PVA photopolymer

C. Close, M. Gleeson, J. Kelly, D. Mooney, J. Sheridan

Proceedings Volume 6335, 63350S (2006) https://doi.org/10.1117/12.681594

KEYWORDS: Diffusion, Polymers, Humidity, Data storage, Holographic data storage systems, Photopolymers, Spatial frequencies, Holography, Polymerization, Magnetism

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Proceedings Article | 13 September 2006 Paper

Nonlocal polymerization driven diffusion model: volume changes during grating formation

John Kelly, Michael Gleeson, Ciara Close, John Sheridan

Proceedings Volume 6335, 63350Q (2006) https://doi.org/10.1117/12.680818

KEYWORDS: Refractive index, Polymers, Diffusion, Modulation, Polymerization, Neodymium, Data modeling, Photopolymers, Diffraction gratings, Holography

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Proceedings Article | 13 September 2006 Paper

Photochemical effects during holographic grating formation in photopolymer using the non-local polymerisation driven diffusion model

Michael Gleeson, Ciara Close, John Kelly, John Sheridan

Proceedings Volume 6335, 63350D (2006) https://doi.org/10.1117/12.681593

KEYWORDS: Polymerization, Polymers, Holography, Molecules, Diffusion, Absorbance, Oxygen, Photopolymers, Absorption, Transmittance

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Proceedings Article | 13 September 2006 Paper

Optimized scheduling technique for holographic data storage

John Kelly, Michael Gleeson, Ciara Close, John Sheridan

Proceedings Volume 6335, 63350J (2006) https://doi.org/10.1117/12.682220

KEYWORDS: Diffraction, Diffraction gratings, Holography, Data storage, Polymers, Data modeling, Diffusion, Polymerization, Photopolymers, Refractive index

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Proceedings Article | 8 September 2006 Paper

Modeling photopolymers for holographic data storage applications

John Sheridan, John Kelly, Michael Gleeson, Ciara Close

Proceedings Volume 6343, 634332 (2006) https://doi.org/10.1117/12.707941

KEYWORDS: Refractive index, Polymers, Polymerization, Modulation, Diffusion, Data modeling, Photopolymers, Holography, Oxygen, Neodymium

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The Nonlocal Polymerization Driven Diffusion model, NPDD, is can be used to describe holographic grating formation in Acrylamide-based photopolymer. The free radical chain polymerization process results in polymer being generated nonlocal both in space and time to the point of chain initiation. Temporal nonlocality can be used to describepost exposure dark effects. Nonlinear response and the effects of dye bleaching have been examined. Both primary and bimolecular chain termination mechanisms have been included and examined. Recently 3-D, and inhibition effects have also been included. In this paper we review of our recent work. It is shown that temporal effects become most notable for short exposres and the inclusion of the nonlocal temporal response function is shown to be necessary to accurately describe the process. In particular, brief post exposure self-amplification of the refractive index modulation is noted. This is attributed to continued chain growth for a brief period after exposure. Following this a slight decay in the grating amplitude also occurs. This we believe is due to the continued diffusion of monomer after exposure. Since the sinusoidal recording pattern generates a monomer concentration gradient during the recording process monomer diffusion occurs both during and after exposure. The evolution of the refractive index modulation is determined by the respective refractive index values of the recording material components. From independent measurements it is noted that the refractive index value of the monomer is slightly less than that of the background material. Therefore as monomer diffuses back into the dark regions, a reduction in overall refractive index modulation occurs. Volume changes occurring within the material also affect the nature of grating evolution. To model these effects we employ a free volume concept. Due to the fact that the covalent single carbon bond in the polymer is up to 50% shorter than the van der Waals bond in the liquid monomer state, free volume is created when monomer is converted to polymer. For each bond conversion we assume a hole is generated which then collapses at some characteristic rate constant. The Lorentz-Lorenz relation is used to determine the overall evolution refractive index modulation and the corresponding diffraction efficiency of the resulting grating is calculated using Rigorous Coupled Wave Analysis (RCWA). The Lorentz-Lorenz relation is used to determine the overall evolution refractive index modulation and the corresponding diffraction efficiency of the resulting grating is calculated using Rigorous Coupled Wave Analysis (RCWA). Inhibition is typically observed at the start of grating growth during which the formation of polymer chains is suppressed. In this paper experiments are reported, carried out with the specific aim of understanding of these processes. The results support our description of the inhibition process in an PVA/Acrylamide based photopolymer and can be used to predict behaviour under certain conditions.

Proceedings Article | 25 April 2006 Paper

Determination of diffusion rates in acrylamide-based photopolymer material

C. Close, M. Gleeson, J. Kelly, F. O'Neill, D. Mooney, J. Sheridan

Proceedings Volume 6187, 61871C (2006) https://doi.org/10.1117/12.663300

KEYWORDS: Diffusion, Polymers, Holography, Data storage, Molecules, Photopolymers, Modulation, Diffraction, Humidity, Refractive index

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Proceedings Article | 25 April 2006 Paper

Photochemical effects during fabrication of holographic gratings in acrylamide-based photopolymer materials

Michael Gleeson, Ciara Close, John Kelly, Feidhlim O'Neill, John Sheridan

Proceedings Volume 6187, 61871D (2006) https://doi.org/10.1117/12.663408

KEYWORDS: Polymerization, Holography, Oxygen, Diffusion, Polymers, Transmittance, Photopolymers, Absorption, Molecules, Plating

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Proceedings Article | 20 April 2006 Paper

Analysis of the temporal effects on grating evolution in photopolymer

John Kelly, Michael Gleeson, Ciara Close, Feidhlim O' Neill, John Sheridan, Sergi Gallego, Cristian Neipp

Proceedings Volume 6187, 618704 (2006) https://doi.org/10.1117/12.663444

KEYWORDS: Refractive index, Polymers, Diffusion, Modulation, Polymerization, Data modeling, Neodymium, Holography, Finite-difference time-domain method, Diffraction

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The nonlocal polymerization driven diffusion model is used to describe holographic grating formation in acrylamidebased photopolymer. The free radical chain polymerization process results in polymer being generated nonlocal both in space and time to the point of chain initiation. A Gaussian spatial material response function and an exponential temporal material response function are used to account for these effects. In this paper we firstly examine the nature of the temporal evolution of grating formation for short recording periods. It is shown that in this case, temporal effects become most notable and the inclusion of the nonlocal temporal response function is shown to be necessary to accurately describe the process. In particular, brief post exposure selfamplification of the refractive index modulation is noted. This is attributed to continued chain growth for a brief period after exposure. Following this a slight decay in the grating amplitude also occurs. This we believe is due to the continued diffusion of monomer after exposure. Since the sinusoidal recording pattern generates a monomer concentration gradient during the recording process monomer diffusion occurs both during and after exposure. The evolution of the refractive index modulation is determined by the respective refractive index values of the recording material components. From independent measurements it is noted that the refractive index value of the monomer is slightly less than that of the background material. Therefore as monomer diffuses back into the dark regions, a reduction in overall refractive index modulation occurs. Volume changes occurring within the material also affect the nature of grating evolution. To model these effects we employ a free volume concept. Due to the fact that the covalent single carbon bond in the polymer is up to 50% shorter than the van der Waals bond in the liquid monomer state, free volume is created when monomer is converted to polymer. For each bond conversion we assume a hole is generated which then collapses at some characteristic rate constant. Incorporating each of these effects into our model, the model is then solved using a Finite-Difference Time- Domain method (FDTD). The Lorentz-Lorenz relation is used to determine the overall evolution refractive index modulation and the corresponding diffraction efficiency of the resulting grating is calculated using Rigorous Coupled Wave Analysis (RCWA). Fits are then carried out to experimental data for 1 second exposures. Good quality fits are achieved and material parameters extracted. Monomer diffusion rates are determined to be of the order of D ~ 10^-10 cm^2/s and the time constant of the nonlocal material temporal response function being of the order of τ_n ~ 10^-2s. Material shrinkage occurring over these recording periods is also determined.

Proceedings Article | 1 September 2005 Paper

The effects of inhibition during grating formation in photopolymer materials

M. Gleeson, J. Kelly, C. Close, F. O'Neill, J. Sheridan

Proceedings Volume 5939, 59390R (2005) https://doi.org/10.1117/12.617675

KEYWORDS: Oxygen, Polymerization, Polymers, Diffusion, Photopolymers, Transmittance, Holography, Absorbance, Differential equations, Molecules

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Proceedings Article | 1 September 2005 Paper

Diffusion rates in non-local photopolymer materials

C. Close, M. Gleeson, F. O'Neill, J. Kelly, D. Mooney, J. Sheridan

Proceedings Volume 5939, 59390Q (2005) https://doi.org/10.1117/12.617639

KEYWORDS: Diffusion, Polymers, Modulation, Photopolymers, Water, Refractive index, Diffraction, Humidity, Spatial frequencies, Diffraction gratings

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Proceedings Article | 1 September 2005 Paper

Investigation of the temporal response and volume changes occurring during grating formation in photopolymer

John Kelly, Michael Gleeson, Ciara Close, Feidhlim O'Neill, John Sheridan

Proceedings Volume 5939, 59390J (2005) https://doi.org/10.1117/12.617272

KEYWORDS: Refractive index, Polymers, Modulation, Diffusion, Polymerization, Neodymium, Diffraction gratings, Diffraction, Holography, Finite-difference time-domain method

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Proceedings Article | 25 August 2005 Paper

Micro-optical elements produced using an photo-embossing technique in photopolymers

Feidhlim O'Neill, Ita Rowsome, Alun Carr, Stephen Daniels, Michael Gleeson, John Kelly, Ciara Close, Justin Lawrence, John Sheridan

Proceedings Volume 5872, 587209 (2005) https://doi.org/10.1117/12.617734

KEYWORDS: Polymers, Photopolymers, Polymerization, X-rays, Diffusion, Optical components, Holography, Absorption, Fabrication, Process modeling

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Proceedings Article | 8 June 2005 Paper

Control and measurement of the physical properties in acrylamide based photopolymer materials

Ciara Close, Michael Gleeson, Feidhlim O'Neill, John Kelly, John Sheridan

Proceedings Volume 5827, (2005) https://doi.org/10.1117/12.605001

KEYWORDS: Refractive index, Diffusion, Polymers, Modulation, Diffraction, Photopolymers, Diffraction gratings, Polymerization, Spatial frequencies, Oxygen

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Proceedings Article | 8 June 2005 Paper

The Impact of Inhibition Processes during Grating Formation in Photopolymer Materials

Michael Gleeson, John Kelly, Ciara Close, Feidhlim O'Neill, John Sheridan

Proceedings Volume 5827, (2005) https://doi.org/10.1117/12.604999

KEYWORDS: Oxygen, Diffusion, Polymerization, Polymers, Photopolymers, Diffraction, Laser beam diagnostics, Holography, Diffraction gratings, Differential equations

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Proceedings Article | 8 June 2005 Paper

Temporal and non-ideal behavior in photopolymers

John Kelly, Michael Gleeson, Ciara Close, Feidhlim O'Neill, John Sheridan, Sergi Gallego, Cristian Neipp

Proceedings Volume 5827, (2005) https://doi.org/10.1117/12.604998

KEYWORDS: Refractive index, Polymers, Neodymium, Diffusion, Photopolymers, Diffraction, Modulation, Polymerization, Data modeling, Holography

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Proceedings Article | 26 October 2004 Paper

Fabrication and testing of holographic gratings

Michael Gleeson, Ciara Close, Feidhlim O'Neill, John Sheridan

Proceedings Volume 5521, (2004) https://doi.org/10.1117/12.560495

KEYWORDS: Diffraction, Modulation, Control systems, LabVIEW, Refractive index, Holography, Laser beam diagnostics, Diffraction gratings, Data processing, Camera shutters

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Showing 5 of 21 publications

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