Abstract
A series of photopolymers based on ethylene glycol phenyl ethyl arylate (EGPEA) monomers and poly(methyl methacrylate) (PMMA) matrix with varying initiator concentrations and sample thicknesses have been synthesized and their optical performance characterized in this study. The advantages of lowering the initiator concentration, including a rather short initiation time within a few seconds; a sharp rising optical response; and a stable saturated diffraction efficiency are demonstrated. The variation in the diffraction efficiency and response time with the exposure energy under various sample thickness and initiator concentrations is examined; a diffraction efficiency as high as 80% and a relatively short response time of 12–39 s are attainable. The dependence of the normalized optical parameter “sensitivity” on the exposure time is depicted, and the peak value of S ranges vastly from about 0.2 to 1.2 × 104 cm/J within a period of 15 s or so, with a maximum value of nearly 1.2 × 104. Favorable evidence of low initiator concentration can further be found when the dependence of the saturated diffraction efficiency with the exposure energy is examined. The data from this study using a low initiator concentration cover a range of exposure energy from 100 to 800 mJ/cm2 and a saturated diffraction efficiency from about 15% to 80%. The successful image reconstruction of 6-membered-ring metal nuts on a hologram based on this EGPEA/PMMA photopolymer system using a reflective holographic recording setup is demonstrated to verify its applicability to holographic storage.
Highlights
Photopolymers have long been considered as crucial materials in developing technology related to photonic applications such as holographic data storage, holographic filters, holographic interferometry, and holographic optical elements [1,2,3,4]
A relatively short initiation time is generally required, during which free radicals are generated from the cleavage of I-784 (Period I). This is followed by a steep rise in the diffraction efficiency, due entirely to the very fast photopolymerization caused by the sequential addition of ethylene glycol phenyl ethyl arylate (EGPEA) monomers to the I-784 free radicals (Period II)
The effect of a low initiator concentration on the optical performance of EGPEA/poly(methyl methacrylate) (PMMA) holographic storage materials has been demonstrated in this study
Summary
Photopolymers have long been considered as crucial materials in developing technology related to photonic applications such as holographic data storage, holographic filters, holographic interferometry, and holographic optical elements [1,2,3,4]. The formation of holographic recording in the photopolymer system is generally attributed to the photo-initiator-induced free radical polymerization of monomers, and they form a phase grating. The initiator concentration has played an instrumental role in deciding the optical performance of the related photopolymers for holographic storage. This can be verified by the two well-known and well-developed systems—i.e., PQ/PMMA and I-784/PMMA. From the viewpoint of better phase grating formation in the holographic film and the better crack-resistance of the photopolymer itself, a commercially available and widely used monomer ethylene glycol phenyl ethyl arylate (EGPEA) was chosen due to its high refractive index and more rigid poly(ethylene glycol phenyl ethyl acrylate) (PEGPEA) that was formed. The I-784 concentrations were at roughly one-twentieth of the reported maximum solubility, and were far less than the widely used concentrations in many photopolymer studies [1,2,5,9,10,11,12,13]
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