GB1342834A - Magnetic-film stripe domain diffraction-grating - Google Patents

Abstract

1342834 Deflecting light SPERRY RAND CORP 19 April 1971 [24 Feb 1970] 22506/71 Heading H4F [Also in Divisions G2 and H1] In a light deflector, parallel magnetic stripe domains capable of providing a variable diffraction grating are produced in a film, e.g. of ferrous alloy, Ni, MnBi, YIG, GdIG, RbNiF 3 , chromium trihalides, EuO, EuSe, by applying thereto and in the plane of the film mutually orthogonal A.C. and D.C. magnetic fields, the direction of the strips being parallel to the D.C. field direction and their width being a function of the D.C. field amplitude and polarity. The A.C. field serves to facilitate the response of the domains to change in the D.C. field by reducing their effective coercivity. As described, the grating is formed (a) by having a Bitter snspension of magnetic particles adjacent the film to align with the strips for a transmission grating; (b) if the film exhibits the Kerr magnetooptic effect, it behaves as a reflection grating to plane polarized light; (c) the film or a coating thereon may exhibit the Faraday effect. Depending on whether one surface of the grating is coated with a reflective metal film (for example the magnetic film itself, if coated with a Faraday effect coating) it will act as a transmission or reflection grating towards polarized light, for example from a He-Ne laser. The D.C. and A.C. fields may be provided by respective pairs of coils mounted on a yoke rotatable about an axis normal to the plane of the film, Fig. 11 (not shown), i.e. to vary the direction of the diffraction grating. In a modification, Fig. 14 (not shown), two pairs of coils apply an A.C. field in the film plane and a variable D.C. field perpendicular to the film. A further coil applies a D.C. field in the film plane and is rotatable (over a limited angle wherein it may still be considered substantially orthogonal to the A.C. field) with respect to the film and the A.C. field, to vary the direction of the stripe domains. The domain width is a function of the perpendicular D.C. field strength. In alternative forms of device, each field may be varied electrically, by adjusting the size and magnitude of two orthogonal components, instead of by mechanical rotation, to vary the stripe domain direction. For the reflection gratings, the field is most easily supplied by strip conductors behind the film. A Kerr reflection grating may replace a laser mirror, or a Faraday Effect transmission grating may be placed between laser mirrors to provide a laser output beam in a controlled direction.