READOUT SYSTEM FOR A MAGNETO-OPTIC MEMORY

• US 3,734,625 A
• Filed: 12/23/1971
• Issued: 05/22/1973
• Est. Priority Date: 09/12/1969
• Status: Expired due to Term

• Current Assignee: Roger L. Aagard
• Original Assignee: Roger L. Aagard
• Inventors: Aagard, Roger L.
• Primary Examiner(s): Bauer, Edward S.
• Application Number:
  US05/211,540
• Time in Patent Office: 516 Days
• Field of Search: 340/174.1M,174YC 356/114,118 350/150,151,DIG.1,DIG.2
• US Class Current: 356/369
• CPC Class Codes: G11B 11/10 using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
• CPC Class Codes: G11B 11/10536 using thermic beams, e.g. lasers

Abstract

An optical mass memory utilizing the Curie point writing technique wherein information is stored on a manganese bismuth film. A laser beam provides thermal energy to a predetermined film spot to achieve Curie point writing. The stored information is retrieved utilizing the polar Kerr magneto-optic effect.

Claims

1. A system for detecting, by the magneto-optic Kerr effect, the magnetic alignment of predetermined spots on a magnetic medium, the system comprising:

a light beam source for projecting a polarized light beam along a first path;

the magnetic medium positioned to receive a light beam at essentially normal incidence and to rotate the polarization direction of the light beam and reflect the light beam back toward the light beam source over essentially the first path;

polarizing beam splitter means located between the light beam source and the magnetic medium, the polarizing beam splitter means being oriented to pass that portion of the projected and reflected light beam having a first polarization direction, and to reflect over a second path a component of the light beam having a polarization direction different from the first polarization direction, the component directed over the second path having a first intensity when the predetermined spot has an anti-parallel magnetic vector alignment and a second, different intensity when the predetermined spot has a parallel magnetic vector alignment;

first light detector means positioned to receive the component directed over the second path;

light deflector means located between the polarizing beam splitter means and the magnetic medium;

focusing means positioned between the light beam deflector means and the magnetic medium for focusing the light beam to a focused light spot at the magnetic medium; and

modulator means positioned between the light beam source and the polarizing beam splitter means.

2. The system of claim 1 and further comprising beam splitter means positioned between the polarizing beam splitter means and the magnetic medium for reflecting a small portion of a light beam reflected from the magnetic medium over a third path;

second light detector means positioned to receive the portion of the light beam directed over the third path, and differential amplifier means for receiving signals from the first and second detector means and for producing an output signal indicative of the difference of the signals.