Magneto-Optic Readout for Computer Memories

Abstract

Experimental measurements have shown that nondestructive magneto‐optic readout from magnetic film computer elements by means of the longitudinal Kerr‐effect can operate at rates of at least one million bits per second. If the steady light source of the magneto‐optic apparatus is sufficiently bright, a signal‐to‐noise ratio of four or better can be obtained from the photomultiplier readout tube. Since the reversal time of thin ferromagnetic films is less than a microsecond, writing speed can be as fast as readout. Information readout from a magnetic film can be obtained by scanning with a high‐intensity light spot. Spurious variations in surface reflectivity of the films are sufficiently small so that parts of the film magnetized in opposite directions can be clearly determined. Experiments with an electronic strobing magneto‐optic method make it possible to observe the details of the magnetization reversal process in very small parts of a film with a time resolution of the order of a nanosecond. Since this strobing process involves sampling and integration, the information bandwidth is too small to be used for digital computer readout. However, this method is useful in studying fine details of the magnetization reversal process. Measurements show that the reversal is repeatable in the different parts of the film.