<title>Erasable Magneto-Optical Laser Mass Memory</title>

Abstract

The scope of this work is to create an alterable and erasable quantum-mechanical laser disc mass memory. The new memory system is based upon optical quantum-mechanical bistability of electron spin systems, created with laser in the ferrimagnetic thin-film (YIG) of a fast rotating Garnet disc (GGG). The microscopic elements of the new memory system are certain photomagnetic cylinder domains and their surrounding, oppositely magnetized toroidal shells. They are characterized either as "black" or "white" electron spin-flips. Electron spin-flips are created near laser focus by means of the angular momentum of an incident, circularly polarized laser beam. In order to create electron spin-flips, the intrinsic ferrimagnetic domains of the Garnet are to be circularly prealigned with laser by thermomagnetic means. The incident laser beam is signal modulated in square waves by means of a linear electro-optical modulator (Pockel's cell), yielding electron spin-reversal (spin-flip) along the concentric thermomagnetically prealigned circular domains of the ferrimagnet. A combined elementary cylinder and its shell comprise a digital photomagnetic electron spin state of plus one (+1), or minus one (-'4), where (h) is Plancks constant divided by 2π. The empty intrinsic state of the cir-cularly prealigned elementary domains comprises the third neutral state zero. Quite different from the optical bistability of volatile semiconductor memories, photo-magnetic bistability is nonvolatile due to the coercive force of the ferrimagnetic thin film. Magnetization stays permanent until it is erased by thermomagnetic means. The theo-retical bandwidth of the new memory is of the order of one (1) Gigahertz, corresponding to the free angular precession frequency of the electron spin-flip, which is determined by the Larmor frequency of the intrinsic magnetization of the ferrimagnetic domains of the Garnet.