%0 Journal Article
%T Overmodulation Control in the Optimization of a H-PDLC Device with Ethyl Eosin as Dye
%A Manuel Ortu£¿o
%A Marina Riquelme
%A Sergi Gallego
%A Andr¨¦s M¨¢rquez
%A Inmaculada Pascual
%A Augusto Bel¨¦ndez
%J International Journal of Polymer Science
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/357963
%X The response of a H-PDLC device is improved by means of a two-step method. First, component optimization¡ªinitiator system, crosslinker, and cosolvent¡ªenables the diffraction efficiency 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 applications due to their properties: higher diffraction efficiency with an acceptable energetic sensitivity. They are easily made at a reduced cost and have great flexibility as holographic recording materials [1¨C4]. The incorporation of liquid crystals adds a special characteristic¡ªthe capacity to vary the electrooptical properties by means of an electric field. The liquid crystal molecules add optical anisotropy to the photopolymer, and therefore it is possible to change the photopolymer response modifying the electric field applied [5¨C10]. Holographic polymer dispersed liquid crystals are known as H-PDLC. They are made by holographic recording in a photopolymerization induced phase separation process (PIPS) in which the liquid crystal molecules diffuse to dark zones in the diffraction grating where they can be oriented by means of an electric field. The orientation of the liquid crystal produces a refractive index variation which changes the diffraction efficiency. Therefore, the grating develops a dynamic behavior that may be modified 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¨C17]. There are many starting criteria for photopolymer optimization: high or low diffraction efficiency, energetic sensibility, low scattering, and so forth. The 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 field, high diffraction efficiency in order to obtain a wide range of responses when the electric field 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. This optimization method takes into account all the previous considerations. The first step is to optimize the component concentrations so as to obtain a high maximum diffraction efficiency ( ) during the recording of the diffraction grating. Initially, the
%U http://www.hindawi.com/journals/ijps/2013/357963/