Three-dimensional optical memory with rewriteable and ultrahigh density using the valence-state change of samarium ions

We report the recording, readout, and erasure of a three-dimensional optical memory using the valence-state change of samarium ions to represent a bit. A photoreduction bit of 200 nm diam can be recorded with a femtosecond laser and readout clearly by detecting the fluorescence as a signal (excitation at 488 nm, 0.5 mW Ar+ laser). A photoreduction bit that is stable at room temperature can be erased by photo-oxidation with a cw laser (514.5 nm, 10 mW Ar+ laser). Since photoreduction bits can be spaced 150 nm apart in a layer within glass, a multilayer structure with several hundred layers could be used to record data. A memory capacity of as high as 1 Tbit could thus be achieved in a glass piece with dimensions of 10 mm×10 mm×1 mm.