Birefringence due to Dislocations in Glide Bands of Rocksalt Single Crystals

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Abstract
Birefringence techniques which emphasize the difference in stress on each side of a slip plane having edge dislocations of one sign are described. The principal stresses due to edge dislocations in a glide band are found to be parallel and perpendicular to the Burgers vector. The opposite stressed regions on both sides of a slip plane produce opposite retardations in the phase of light passing through the slip plane. When this light is retarded in phase by an amount equal to the advancement from the compressive region (or advanced by an amount equal to the retardation from the tensive region), a birefringence band forms which is, for instance, dark on the compressive side, light on the tensive side in a background having an intensity halfway between these two shades. These asymmetrically shaded birefringence bands are observed when viewed both normal and parallel to the Burgers vector and this is shown to be a direct consequence of the edge dislocations in the slip planes and to be independent of screws. The asymmetry of the band permits a determination of the sign of the dislocations in the slip plane and the apparent position of its source. The magnitude of the principal stress parallel to the Burgers vector was computed from the measured retardations and found to be in good agreement with that computed from the dislocation stress fields.

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