摻雜式PMMA感光高分子的製備及其在體積全像資訊儲存上的特性研究

Abstract

本論文主要致力於發展一種具低光致收縮效應的摻雜式PMMA感光高分子材料，並且探討它在體積全像資訊儲存上的特性表現。首先我們闡述材料之設計概念，以及如何製備出PQ/PMMA 體積全像記錄塊材，並以不同的光學實驗來探討所製備材料在體積全像資料儲存上特別重要的的特性，包含光學特性、動態儲存範圍、材料敏感度和曝光後尺度穩定性…等性質，進一步以多工儲存技術在厚塊材中儲存多張影像並且重建之，由清晰無扭曲的影像品質可看出曝光收縮量很小。根據寡單體之光聚合擴散模型，可預測材料所記錄的體積全像具有暗反應自我顯影之特性，並且經過後曝光處理可定影。 為了彌補PQ/PMMA 之動態範圍和敏感度先天上的不足，因此我們提出兩種改善全像記錄特性的方法：(1)在PQ 分子結構上導入它種官能基團，試圖影響其光反應速度以改變材料之全像特性。(2)摻雜它種壓克力型單體與MMA 分子形成共聚合高分子基底，藉由高反應性與多反應端點之殘存單體來提升光反應物種間的結合能力。實驗結果顯示，染料加入長鏈烷基之推電子官能基團以及摻雜多反應端點壓克力單體之共聚合系統，可較有效地改善材料之動態範圍與敏感度。 最後，我們發展了PQ/PMMA 更獨特的全像記錄行為，即偏振全像與雙波長全像記錄，對於2mm 厚樣品的特性分析結果顯示：(1)在514nm 線偏光誘發下可引發約1.2×10-5 的雙折射率變化；若以正交圓偏光記錄偏振全像，繞射效率可到達40%，從布拉格選擇率可看出全像光柵幾乎沒有收縮。最後展示以偏振多工方式儲存與重建全像光學圖案。(2)利用光閘光源(325nm 紫光)/寫入光源(647nm 紅光)的雙波長記錄架構，可成功地在材料上記錄全像；在有光閘光源開啟下，可增加104 倍的紅光材料敏感度與繞射效率，其最高繞射效率約4%。上述之偏振全像、可延伸記錄波長(紅光或紅外光)以及選擇性記錄特性都表示PQ/PMMA 在做為體積全像的繞射與濾波元件的應用上，具有更多的想像空間和潛力。

In this dissertation, we focus on the holographic characterization of the doped PMMA photopolymer for volume holographic data storage. First of all, we elaborate the design strategy and preparation technique to fabricate a photopolymer with low photochemical shrinkage, called phenanthrenequinone doped poly(methylmethacrylate) (PQ/PMMA). The high-priority material requirements for holographic data storage, including optical characteristics, dynamic range (M#), sensitivity and photo-induced dimensional stability, are investigated on it. An experimental demonstration of multiple storage of digital data pages with non-distorted readout is presented. Based on the diffusion model of holographic recording in PQ/PMMA, the recoded volume holograms are predicted to be self-developed in dark and fixed by optical exposure. These results indicate that the PQ/PMMA can be considered as a promisingmaterial for volume holographic data storage application. However, the related characterization of PQ/PMMA such as dynamic range and sensitivity still need to be improved. From our previous research on physical mechanism of holographic recording in PQ/PMMA, the refractive index modulation between the bright and dark zones of interference patterns, is attributed to the adduct of one PQ molecule with one MMA molecule in the bright zone. Therefore, we proposed two methods to improve the holographic characteristics of the material： (1) By introducing different functional groups on the side-chain of PQ molecule, the holographic characteristics of the material can be modified. We found that, by selecting appropriate functional groups, an improvement in sensitivity and M# for holographic data storage can be achieved. (2) By co-doping different acrylate-based monomer in the PMMA matrix, holographic characteristics of the material can also be modified. We anticipated that the co-doped multi-acrylate /highly reactive monomers can enhance the combination ability of monomer molecules with PQ radicals, as well as the sensitivity and M#. Further, we found that the planar structure of PQ molecules dispersed in amorphous PMMA polymer possessed the photo induced anisotropy with linear polarized light. The resulting photo-induced birefringence in a 2-mm thick sample is measured by a phase-modulated ellipsometry, which can reaches 1.2 x10-5 by linearly polarized beam at 514 nm. We have also performed volume polarization holographic recording with two different polarization configurations. The experimental results show that with circular polarization configuration, the maximal diffraction efficiency of hologram can reach ~40%. A clear sinc-squared Bragg selectivity curve has been obtained so that the shrinkage is not a suspect in our PQ/PMMA photopolymer. The capability of multiplexing polarization holograms in our PQ/PMMA samples is also tested. These results suggest our PQ/PMMA can be attractive candidate for permanent volume polarization holographic recording. Due to the negligible shrinkage effect and good long-term stability of PQ/PMMA photopolymer, it is suitable to record the volume holographic hologram as narrow-bandwidth filter for optical communication and bio-sensing application. Unfortunately, the material can be used at only a limited spectral range shorter than 550 nm. In terms of chemical formula, the PQ is a-diketone based derivatives so that using the same idea proposed by Brauchle et al., it is possible to perform two-wavelength recording. Then, we investigated the two-wavelength holographic recording in 2-mm thick PQ/PMMA. The hologram was recorded at 647 nm in the sample with gating by an additional laser at 325 nm, significant 104-fold increase in material sensitivity and diffraction efficiency is achieved. The maximal diffraction efficiency can reach ~4%. In addition, Bragg selectivity curve and ability for image reconstruction is demonstrated in a 2-mm thick sample supporting further applications as recording media for volume holographic device with extended spectral response and selective recording property.