Ms. Ciara E. Close Profile

Ms. Ciara E. Close

Student at Univ College Dublin

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Author

Publications (21)

PROCEEDINGS ARTICLE | May 15, 2010

Using short exposures to approximate diffusion rates

Proc. SPIE. 7717, Optical Modelling and Design

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

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PROCEEDINGS ARTICLE | May 14, 2010

Approximating monomer diffusion in the Raman-Nath regime

Proc. SPIE. 7717, Optical Modelling and Design

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

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PROCEEDINGS ARTICLE | April 25, 2008

Improvement of photopolymer materials for holographic data storage

Proc. SPIE. 6994, Photon Management III

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

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PROCEEDINGS ARTICLE | September 27, 2007

Photopolymer materials for holographic data storage applications

Proc. SPIE. 6698, Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications

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

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PROCEEDINGS ARTICLE | September 27, 2007

Photopolymer material used in the recording of slanted gratings

Proc. SPIE. 6698, Photonic Fiber and Crystal Devices: Advances in Materials and Innovations in Device Applications

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

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PROCEEDINGS ARTICLE | September 13, 2006

Nonlocal polymerization driven diffusion model: volume changes during grating formation

Proc. SPIE. 6335, Organic Holographic Materials and Applications IV

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

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PROCEEDINGS ARTICLE | September 13, 2006

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

Proc. SPIE. 6335, Organic Holographic Materials and Applications IV

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

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PROCEEDINGS ARTICLE | September 13, 2006

Optimized scheduling technique for holographic data storage

Proc. SPIE. 6335, Organic Holographic Materials and Applications IV

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

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PROCEEDINGS ARTICLE | September 13, 2006

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

Proc. SPIE. 6335, Organic Holographic Materials and Applications IV

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

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PROCEEDINGS ARTICLE | September 8, 2006

Modeling photopolymers for holographic data storage applications

Proc. SPIE. 6343, Photonics North 2006

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

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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 | April 25, 2006

Determination of diffusion rates in acrylamide-based photopolymer material

Proc. SPIE. 6187, Photon Management II

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

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PROCEEDINGS ARTICLE | April 25, 2006

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

Proc. SPIE. 6187, Photon Management II

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

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PROCEEDINGS ARTICLE | April 20, 2006

Analysis of the temporal effects on grating evolution in photopolymer

Proc. SPIE. 6187, Photon Management II

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

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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 | September 1, 2005

Diffusion rates in non-local photopolymer materials

Proc. SPIE. 5939, Organic Holographic Materials and Applications III

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

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PROCEEDINGS ARTICLE | September 1, 2005

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

Proc. SPIE. 5939, Organic Holographic Materials and Applications III

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

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PROCEEDINGS ARTICLE | September 1, 2005

The effects of inhibition during grating formation in photopolymer materials

Proc. SPIE. 5939, Organic Holographic Materials and Applications III

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

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PROCEEDINGS ARTICLE | August 25, 2005

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

Proc. SPIE. 5872, Advancements in Polymer Optics Design, Fabrication, and Materials

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

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PROCEEDINGS ARTICLE | June 8, 2005

Temporal and non-ideal behavior in photopolymers

Proc. SPIE. 5827, Opto-Ireland 2005: Photonic Engineering

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

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PROCEEDINGS ARTICLE | June 8, 2005

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

Proc. SPIE. 5827, Opto-Ireland 2005: Photonic Engineering

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

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PROCEEDINGS ARTICLE | June 8, 2005

The Impact of Inhibition Processes during Grating Formation in Photopolymer Materials

Proc. SPIE. 5827, Opto-Ireland 2005: Photonic Engineering

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

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PROCEEDINGS ARTICLE | October 26, 2004

Fabrication and testing of holographic gratings

Proc. SPIE. 5521, Organic Holographic Materials and Applications II

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

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Showing 5 of 21 publications

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