Analyses for the Dynamics of Two-Center Holographic Recording and their Applications

双中心全息记录技术具有非挥发性、全光性、实时实地性等优点，因而成为一种非常实用化的全息记录技术。但该技术是一直缺乏精确描述其动力学过程的解析解，同时也缺乏适用于三维全息记录情况的矢量动力学分析，此外该方案还存在衍射效率较低和响应速度较慢等影响其实际应用的问题。本论文论述了作者对双中心全息记录在矢量动力学分析、记录结构与方案的优化、灵敏度分析，以及光折变体光栅元件实用性演示系统等方面理论和实验上的一些工作，主要内容包括： （1）对描述双掺杂晶体非挥发性全息记录动力学过程的Kukhtarev方程进行了矢量分析，分析中考虑了体光生伏特效应和外加电场的作用。在小信号近似的基础上给出了双中心全息记录中记录与固定阶段空间电荷场的矢量时间解析解，并且可以方便地简化为单中心记录的矢量解析解。基于矢量解析解对双中心全息记录的特性进行了分析。在综合考虑空间电荷场的各向异性以及晶体有效电光系数的各向异性后，分别给出了LiNbO3:Fe:Mn晶体双中心全息记录两种典型记录方案的优化记录方向。 （2）对双中心全息记录的记录灵敏度进行了研究，修改了单中心全息记录的灵敏度定义以适用于双中心全息记录。基于双掺杂晶体Kukhtarev方程组的时间解析解给出了双中心全息记录的灵敏度的解析表达式。为了方便与单中心全息记录方案相比较，同时综合描述深、浅掺杂中心的电子竟争效应，提出了有效电子迁移长度，该有效电子迁移长度是随记录光强与固定光强之比而变化的。分析表明双中心全息记录中较低的灵敏度来自于较低的未激发浅中心施主浓度与较短的有效电子迁移长度。 （3）对光折变全息记录特别是双中心全息记录中90度记录结构下较低的衍射效率进行了研究，采用局域衍射理论对90度记录结构的衍射进行了分析。分析显示在同样的折射率变化和光束宽度的情况下，只有当折射率光栅振幅大于10－4时，90度记录结构衍射效率才能够与小角度透射记录结构的衍射效率大致相当。针对环境干扰导致的干涉条纹振动影响光栅记录，提出了有效调制度概念，根据分析大角度记录结构的干涉条纹间距很小，容易受外界环境干扰而导致低的折射率变化率，因此在大角度体光栅记录实验中应采用主动条纹锁定系统，并且稳定效果必须超过一定阈值。此外在LiNbO3:Fe:Mn晶体双中心90度全息记录中，即使采用优化的微观光学参量，633nm记录光的光束宽度也应大于6mm。 （4）为了验证光折变三维体全息元件在通信领域的潜在应用价值，设计制作了一套利用光折变三维体全息元件作为信号光接收及波面变换器件的激光通信实时图像演示系统，自行研制了具有多种用途的光接收终端，验证了光折变三维体全息元件对图像载波激光信号的传输与波面变换能力。The two-center holographic recording method has become a very practical holographic recording technology because of its merits in nonvolatile holographic recording, all-optical recording/fixing, and in-situ processing. However, it have lacked a perfect analytical solution for the dynamics in recording and fixing phase, and it also have lacked a vectorial analyses for three-dimensions holographic recording. Furthermore, in practical applications, this scheme still has some important problems, such as lower diffraction efficiency, slower response velocity, and so on. In this dissertation, vectorial analyses for the dynamics of two-center holographic recording in writing and fixing phase, the optimizations of recording geometry, the analyses of recording sensitivity, and a demo system for the applicable ability of the photorefractive volume holographic elements are presented: (1) Vectorial Kukhtarev equations modified for the nonvolatile holographic recording in doubly doped crystals are analyzed, in which the bulk photovoltaic effect and the external electrical field are both considered. On the basis of small modulation approximation, both the analytic solutions to space-charge field with time in the recording phase and in the readout phase are deduced. The analytic solutions can be easily simplified to adapt the one-center model and have the same analytic expressions as given ones when the grating vector is along with the optical axis. Considering the anisotropy of the space-charge field and the effective electro-optic coefficient, two optimal recording directions are given to maximize refractive index change in doubly doped LiNbO3 :Fe:Mn crystals for two typical recording methods, respectively. (2) The photorefractive sensitivity defined for single-center holographic recording is modified to adapt the two-center holographic recording. Based on the time analytic solution of Kukhtarev equations for doubly doped crystals, the analytic expression of photorefractive sensitivity is given. For comparing with single-center holographic recording and summing the electron competition effects between the deeper and shallower traps, an effective electron transport length is proposed, which vary with the intensity ratios of recording light to sensitive light. According to our analyses the lower photorefractive sensitivity in two-center holographic recording is mainly due to the lower concentration of unionized dopants in shallower center and the shorter effective electron transport length. (3) Basing on the theory of local diffraction in volume grating with finite size, we study the lower diffraction efficiency in two-center holographic recording with 90-degree geometry. It shows that the diffraction efficiency in 90-degree geometry would be comparable with that in transmission geometry only when the amplitude of refractive grating is more than 10-4 with the same refractive index change and the same beams widths. According to the effects of fringe vibration caused by environment perturbation in holographic recording, an effective modulation depth is proposed. Narrow grating space in large-angle recording geometry makes it more sensitive to ambient disturbs and leads to lower effective modulation depth, hence the lower refractive index change. For obtaining higher diffraction efficiency in experiments with large-angle geometry an active stabilization system is necessary and some threshold values must be met. Furthermore, though the optimal microcosmic optical parameters are met for two-center holographic recording with 633nm in LiNbO3 :Fe:Mn crystals, the widths of recording beams must be over 6mm. (4) For demonstrating the potential applications of the photorefractive 3D volume holographic elements in communication system, a demo system for in-satu video transmissions with laser carriers is designed and a multi-useful optical receiver is developed by us, where the photorefractive 3D volume holographic element perform some important functions of receiving and wavefront transform of laser carrier. It verifies the ability of the photorefractive 3D volume holographic elements to transmit and transfer the laser carrier with video signal