Doubly doped lithium niobate overcomes erasure problem with holographic storage
Researchers at the California Institute of Technology (Pasadena, CA) demonstrated a nonvolatile holographic data-storage technique that could lead to rewritable holographic memory. Demetri Psaltis and fellow researchers used a 0.85-mm-thick crystal of lithium niobate doped with iron and manganese. A 100-W mercury lam¥illuminated the crystal evenly with unpolarized ultraviolet (UV) light at 365 nm. Two 633-nm beams from a single 35-mW HeNe laser interfered at the crystal for holographic recording.
The team illuminated the crystal with the red and UV light at the same time--the red light records a pattern in the iron by exciting electrons within it, while the UV light excites electrons from both the iron and the manganese. The excited electron distribution and current patterns are replicas of the red-light intensity pattern; thus the manganese stores the same pattern as the iron. When the pattern is read with red light, it is washed out from the iron but remains in the manganese, so it is not erased. Adding UV light again allows the pattern in the manganese to be erased and rerecorded.