Low temperature optical beam - Addressable memory

Work on a low temperature laser beam addressable memory will be presented. There are several advantages for a beam addressable memory below 77°K. First, the memory medium, an EuO film gives large magneto-optic effects which result in a fast read out rate. Second, at a low operating temperature, the specific heat of the material is small since the lattice and electronic specific heats are proportional to T³and T, respectively. Thus, thermo-writing requires much less energy at low temperature than at room temperature. Third, because of the low energy requirement for the read-write transducer, injection lasers with fast switching speeds can be used. Fourth, the films that were investigated can sustain small area magnetization reversals. Using injection lasers as transducers and EuO films as memory storage elements, reading and writing experiments were carried out. Bits of < 3µ in diameter were written with a 10 mw laser in 10 nanosecond by using thermal writing. The laser energy required to write such a bit is 10^-3ergs; and since no substantial magnetic spread was observed in a thin film of EuO, the density of packing is essentially limited by optics. A packing density of 10⁷bits/cm²seems achievable. High speed reading experiments were also carried out. Since the magneto-optic conversion efficiency is very high, a good S/N ratio for detection was achieved by a 1-mw laser pulse of a few nanoseconds duration.