Comparison of the recording dynamics of phenanthrenequinone-doped poly(methyl methacrylate) materials

Abstract

A comparative analysis of phenanthrenequinone-doped poly(methyl methacrylate) materials fabricated at California Institute of Technology and National Chiao Tung University is performed in order to understand the dierences exhibited in their recording and baking dynamics. Ó 2001 Published by Elsevier Science B.V.Keywords: Holography; Photopolymer material; PQ-PMMA; Grating dynamics; Temperature eect Phenanthrenequinone-(PQ-) doped poly(methyl methacrylate) (PMMA) [1,2] has been used as a recording material in optical memories and other holographic systems [3±6]. This material consists of a polymeric basis doped with chromophores, the PQ molecules. This material is lightweight and durable, and does not suer from shrinkage. High optical quality samples of dierent shapes and thicknesses can be obtained. These properties make it an excellent candidate for holographic memory modules. In this paper, we compare the PQ±PMMA samples that we use at California Institute of Technology (Caltech) with those fabricated at National Chiao Tung University (NCTU) and try to understand the dierences in behavior they exhibit.Sample preparation consists of dissolving PQ molecules ( 6 0.7%) in liquid methyl methacrylate (MMA) together with azo-bis-isobutyrolnitrile, a polymerization thermal initiator. This solution is poured into molds and allowed to polymerize in a pressure chamber. The preparation process followed at Caltech diers from the one followed at NCTU in the temperature at which the pressure chamber is set during polymerization. For the Caltech material, the temperature of the chamber is set to 80°C. On the other hand, at NCTU the polymerization process is split into two steps [4,7]. First, the solution is let to rest at room temperature for approximately 120 h until the solution turns homogeneously viscid. At this point, the

Two-wavelength holographic recording in photopolymer using four-energy-level system: experiments and modeling

“…In holographic recording, the writing time is in the order of 1000 min. The diffusion length of PQ molecules in PMMA matrix at room temperature can be calculated to be in the order of submicrometers, [30][31][32] which is a fraction of typical fringe spacing of the interference fringe. Hence, the spatial modulation of the hologram will be affected.…”

PQ/PMMA photopolymer: Modelling post-exposure

“…We also note that the amount of MMA remaining in the material layer can affect the behavior of the material. In a previous paper it was reported that PQ can act as photointiator of polymerization, where there is a significant excess of residual monomer [21]. In this case, the photoactivated PQ molecules act as initiators of the polymerization before they eventually attach to MMA, which can produce a substantial modulation of the index of refraction [21].…”

“…It is important to note that the process used to produce the layers, (not only their composition) can have dramatic impact on how it reacts during exposure. For example the use of spin coating out of a solvent like toluene, bulk polymerized in a mold, or free radical polymerization at multiple conditions [21], will all lead to different responses. However we also wish to emphasize that while the simulations performed in this paper are carried out using physical parameter values from [13,14], the results presented should be of at least qualitative relevance for PQ/PMMA materials in general (not just a specific type).…”

“…In a previous paper it was reported that PQ can act as photointiator of polymerization, where there is a significant excess of residual monomer [21]. In this case, the photoactivated PQ molecules act as initiators of the polymerization before they eventually attach to MMA, which can produce a substantial modulation of the index of refraction [21]. As a result, the final (stable) grating is due to the modulation of index caused by the polymerization of monomer in the illuminated areas, as well as by the fraction of PQ that attached to the PMMA [21].…”

“…In this case, the photoactivated PQ molecules act as initiators of the polymerization before they eventually attach to MMA, which can produce a substantial modulation of the index of refraction [21]. As a result, the final (stable) grating is due to the modulation of index caused by the polymerization of monomer in the illuminated areas, as well as by the fraction of PQ that attached to the PMMA [21]. However, in this paper, we assume that the material used has been purified before illumination.…”