【作者】 孔芳；

【导师】 江竹青；

【作者基本信息】 北京工业大学 ， 光学， 2006， 硕士

【摘要】 体全息存储技术以其在存储容量和存储速率上的独特优势,成为颇具潜力的下一代存储技术,而光折变记录材料（如掺杂的LiNbO3晶体）则以其大的动态范围及易于大尺寸生产等特性成为体全息存储的一种非常重要的存储材料。但是用光折变材料进行体全息存储时,读出光对已记录光栅的擦除,即光折变光栅读出时的易失性是一个不可忽视的问题。迄今为止,已经有多种全息固定技术被提出,如热固定技术和电固定技术,但是由于这些技术不能满足实时、快速擦除等方面的要求而阻碍了全息方法读写信息的实用性发展。采用具有深浅两个掺杂中心的双掺铌酸锂晶体,一种全光过程的双色体全息的光固定技术被提出并成为了一种最具潜力的体全息存储固定技术。在进行双色体全息存储时,具有高光子能量的敏化光（本论文中为紫外光）首先激发深能级的电子通过导带到达浅能级中心,从而使晶体变得对低光子能量的记录光敏感。当干涉的记录光照射到晶体上时,由于门光束的同时存在,信息同时存储在深浅两个能级。在读出时,由于只有低光子能量的光存在,所以只有被存储在浅能级的信息被擦除,而深能级由于对读出光不敏感,其中记录的信息被保留,从而实现全息存储的非易失性读出。本论文对双掺LiNbO₃:Fe:Cu晶体中的非易失性全息存储的内在物理机制进行了理论上的分析,并对双色的记录和固定过程进行了分析讨论,确定了双色存储过程的三步记录方案:首先用敏化光对晶体进行一定时间的敏化,然后用干涉的记录光和非干涉的门光束同时进行记录,记录完毕后,用沿布拉格角度方向的单束记录光进行固定读出。我们通过一系列实验对LiNbO₃:Fe:Cu晶体中的双色全息存储的条件进行了优化,确定了在LiNbO₃:Fe:Cu晶体中进行双色全息存储时最佳的敏化程度及记录光与门光束的光强比（I_w /I_g）。实验结果表明,在紫外光的敏化光强是305mw/cm2,敏化时间为20分钟左右,I_w /I_g=14时,取得了较好的全息存储性能,得到了η=31%的饱和衍射效率, S=0.016 cm / J的记录灵敏度。本论文还对LiNbO₃:Fe:Cu晶体进行角度复用的曝光特性进行了分析讨论,并用简单的曝光时序实现了50幅全息图等衍射效率的双色存储,得到的平均记录灵敏度S_ave=0.009 cm / J,固定后动态范围不小于4.7。并首次成功实现了10幅图像的全息存储,并对其噪声的特点进行了初步的分析。更多还原

【Abstract】 Volume holographic storing （VHS） is a promising technique for next generation data storage owning to its high storage density and high data transfer rates. Photorefractive materials （e.g., doped LiNbO3） have been considered as one kind of the most important materials for VHS with their advantages of wider dynamic range and commercial availability in large size. But in these normal cases, readout always results in the erasure of recorded information, known as volatility of photorefractive gratings. Although several techniques for fixing holograms, such as thermal fixing and electrical fixing, have been developed, it is difficult to implement these techniques in real time, and impossible for rapid optical refreshment of memory. These drawbacks affect the practical process of holographic read-write memories. By using doubly doped LiNbO3 crystals with deep-doped center and shallow-doped center, nonvolatile holographic storage can be achieved in an completely optical way.In such two-center holographic technique, sensitizing light of high photon energy （UV light） excites electrons of deep traps to shallow center via conduction band, so that the material is sensitive to the recording lights of low photon energy. During the recording with two coherent beams producing spatially modulated light pattern, the recording medium is sensitized simultaneously by UV light, so that the holograms are both stored in the shallow center and deep center. Since light of low photon energy is only able to erase the holograms recorded in the shallow center, and the holograms in the deep center are left that is insensitive to red light for further readout, thus the nonvolatile volume holographic storage is realized.We studied theoretically the inherent mechanisms of nonvolatile holographic storage in doubly doped LiNbO3:Fe:Cu crystals. The two-color recording and fixing processes are analytically discussed. Three-step recording scheme is made: firstly, illuminate the crystal with UV light to sensitize it for some time, then record holograms with two coherent beams as recording light and a homogeneous UV beam as sensitizing light ,finally fix the hologram with single homogeneous recording beam at the Bragg angle.We performed a series experiments to find out the optimization of two-color holographic recording in LiNbO₃:Fe:Cu crystals. The optimum parameters of更多还原