Hindawi Publishing Corporation International Journal of Polymer Science Volume 2013, Article ID 357963, 8 pages http://dx.doi.org/10.1155/2013/357963 Research Article Overmodulation Control in the Optimization of a H-PDLC Device with Ethyl Eosin as Dye Manuel Ortuño, 1,2 Marina Riquelme, 1 Sergi Gallego, 1,2 Andrés Márquez, 1,2 Inmaculada Pascual, 1,3 and Augusto Beléndez 1,2 1 Instituto Universitario de F´ ısica Aplicada a las Ciencias y las Tecnolog´ ıas, Universidad de Alicante, Apartado 99, 03080 Alicante, Spain 2 Departamento de F´ ısica, Ingenier´ ıa de Sistemas y Teor´ ıa de la Se˜ nal, Universidad de Alicante, Apartado 99, 03080 Alicante, Spain 3 Departamento de ´ Optica, Farmacolog´ ıa y Anatom´ ıa, Universidad de Alicante, Apartado 99, 03080 Alicante, Spain Correspondence should be addressed to Manuel Ortu˜ no; mos@ua.es Received 9 September 2013; Accepted 22 October 2013 Academic Editor: Michael J. Bojdys Copyright © 2013 Manuel Ortu˜ no et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. he response of a H-PDLC device is improved by means of a two-step method. First, component optimization—initiator system, crosslinker, and cosolvent—enables the difraction eiciency of the hologram to be maximized. Second, the use of N-methyl-2- pyrrolidone in combination with N-vinyl-2-pyrrolidone prevents the overmodulation in photopolymers containing ethyl eosin. 1. Introduction Nowadays, photopolymers are used in holographic applica- tions due to their properties: higher difraction eiciency with an acceptable energetic sensitivity. hey are easily made at a reduced cost and have great lexibility as holographic record- ing materials [1–4]. he incorporation of liquid crystals adds a special characteristic—the capacity to vary the electrooptical properties by means of an electric ield. he liquid crystal molecules add optical anisotropy to the photopolymer, and therefore it is possible to change the photopolymer response modifying the electric ield applied [5–10]. Holographic polymer dispersed liquid crystals are known as H-PDLC. hey are made by holographic recording in a photopolymerization induced phase separation process (PIPS) in which the liquid crystal molecules difuse to dark zones in the difraction grating where they can be oriented by means of an electric ield. he orientation of the liquid crystal produces a refractive index variation which changes the difraction eiciency. herefore, the grating develops a dynamic behavior that may be modiied by means of an electronic device. In this manner, it is possible to make dynamic devices such as tunable-focus lenses, sensors, phase modulators, or prism gratings [11–17]. here are many starting criteria for photopolymer opti- mization: high or low difraction eiciency, energetic sen- sibility, low scattering, and so forth. he objective of a H- PDLC material is to act as a support for an electrooptical dynamic device. Bearing this in mind, the material must have the following properties: low thickness for a low electric ield, high difraction eiciency in order to obtain a wide range of responses when the electric ield is applied, and low scattering to prevent optical deformations. In order to achieve these properties, we propose a two-step method that may help other researchers to obtain an optimized material quickly and easily. his optimization method takes into account all the previous considerations. he irst step is to optimize the component concentrations so as to obtain a high maximum difraction eiciency (DE max ) during the recording of the difraction grating. Initially, the monomer, liquid crystal, and thickness of the layer are selected. he liquid crystal concentration is then set to a ixed value and the concentrations of dye, initiator, crosslinker, and cosolvent are optimized in order to obtain a high DE max . he variation in each component concentration within a speciic range allows the inluence of that particular component on the photopolymer to be studied. he components are optimized in the following order: dye, initiator, crosslinker,