Persistent holographic storage in photorefractive crystals

Abstract

The work presented in this thesis has been focused on solving the most important and long-lasting problem of destructive read-out in holographic recording in photorefractive crystals. Several interesting methods for solving this problem were proposed and demonstrated by researchers for more than two decades. However, none of them were practical for read / write applications. The most promising all-optical method, which is still being pursued by some researchers, was two-step recording. However, the method suffers from low sensitivity and dynamic range, even in the optimized conditions. Furthermore, several experimental results were not explained due to the lack of a complete understanding of the dominant phenomena that were involved. Our strategy in solving the problem of destructive read-out of holograms was to first provide a complete understanding of the physics of the two-step recording method by appropriate modeling, and to explain the experimental results that had not been explained before. Such an understanding gave us a good idea about the major problem of the method, and we were able to find a solution to that problem by adding one dopand to the recording crystal. The method we developed both theoretically and experimentally in this thesis is called two-center holographic recording. The initial results of the method (without any optimization) offer more than one order of magnitude (and for some parameters, two orders of magnitude) improvement over the optimized two-step recording method. In this thesis, we provide a complete modeling for two-center recording that agrees very well with the experimental results, provides us with the understanding of the main physical phenomena that are involved, and helps us in optimizing the method. The next step is to relate the material and system parameters for the system design. We present in this thesis a standard framework for such a relation, and outline the main general steps in the system design using two-center recording. The idea developed in this thesis opens us several avenues for further thinking and research, and some of them are already being investigated by different research groups.