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Of the several configurations that have been proposed and studied for the implementation of a high-density, fast- access volume holographic memory system, a 90 degree(s) angular multiplexing configuration that uses a 45 degree(s)-cut iron- doped lithium niobate (LNB:Fe) crystal has attracted much attention in the last few years. In a recent paper, Burr and Psaltis have used this configuration to show that the diffraction efficiency ((eta) ) of each hologram can be estimated by (eta) equals (M/#/N)2, where N is the total number of angular-multiplexed holograms, and that the system parameter (M/#) can be determined by monitoring the recording and erasure dynamic of just one hologram. In addition, the authors have presented a mathematical expression which relates M/# to the photorefractive properties of the holographic material, the intensities of the recording beams and the recording geometry. We have applied the techniques (of Burr and Psaltis) to study a spatial and angular multiplexing configuration in the 90 degree(s) geometry. In this approach the angular multiplexing is combined with the spatial multiplexing technique by partitioning the crystal into a vertical array of `NL' layers, and each layer into a horizontal array of `NC' cells. If each cell can accommodate `N' holograms (by angular multiplexing, for example), then the total number of holograms recorded in the sample becomes N X NL X NC. In this paper, we present the theoretical and experimental results on cell-to-cell variation in M/# within a layer. Our results indicate that the cell-to-cell variation in the M/# can be reduced at the cost of a lower average M/# and a longer recording time. Advantages and limitations of both the theoretical model and the experimental techniques are discussed.
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