Analysis of the temporal effects on grating evolution in photopolymer
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Título: | Analysis of the temporal effects on grating evolution in photopolymer |
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Autor/es: | Kelly, John V. | Gleeson, Michael R. | Close, Ciara E. | O'Neill, Feidhlim T. | Sheridan, John T. | Gallego, Sergi | Neipp, Cristian |
Grupo/s de investigación o GITE: | Holografía y Procesado Óptico |
Centro, Departamento o Servicio: | Universidad de Alicante. Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal | University College Dublin. Department of Electronic and Electrical Engineering |
Palabras clave: | Holography | Holographic recording materials | Photopolymers | Volume holograms |
Área/s de conocimiento: | Óptica | Física Aplicada |
Fecha de creación: | 2006 |
Fecha de publicación: | 20-abr-2006 |
Editor: | SPIE, The International Society for Optical Engineering |
Cita bibliográfica: | KELLY, John V., et al. "Analysis of the temporal effects on grating evolution in photopolymer". En: Photon management II : 3-4 April, 2006, Strasbourg, France / edited by John T. Sheridan, Frank Wyrowski. Bellingham, Wash. : SPIE, 2006. (Proceedings of SPIE; Vol. 6187). ISBN 978-0-81946-243-5, pp. 618704-1/8 |
Resumen: | 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 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. 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 cm2/s and the time constant of the nonlocal material temporal response function being of the order of τn ~ 10-2s. Material shrinkage occurring over these recording periods is also determined. |
Patrocinador/es: | Support of enterprise Ireland and Science Foundation through the Research Innovation Fund, the Basic Research Program and the Research Frontiers Program and of the Irish Research Council for Science, Engineering and Technology. |
URI: | http://hdl.handle.net/10045/9704 |
ISBN: | 978-0-81941-624-35 |
ISSN: | 0277-786X |
DOI: | 10.1117/12.663444 |
Idioma: | eng |
Tipo: | info:eu-repo/semantics/article |
Derechos: | Copyright 2006 Society of Photo-Optical Instrumentation Engineers. This paper was published in Proceedings of SPIE, vol. 6187, and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. |
Revisión científica: | si |
Versión del editor: | http://dx.doi.org/10.1117/12.663444 |
Aparece en las colecciones: | INV - GHPO - Artículos de Revistas |
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