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Abstract

A method is disclosed for hot press-forging a normally frangible optically integral crystalline mass ('optical body') in a closed die, by directly pressing a surface of the mass while it is peripherally surrounded by a crystal powder the amount of which is computed from the deformation ratio desired and the geometry of the die. The crystal powder is compacted by the non-uniformly directed forces transmitted to it by the optical body, and eventually the crystal powder is sufficiently dense so as dynamically to constrain the optical body at its peripheral surface. The dynamic constraint of the optical body while it is being forged is effected in such a way as to permit deformation of the optical body without fracturing it, and, without affecting its optical integrity. Hot press-forging the optical body by peripherally surrounding it with the crystal powder produces a stress environment in which the forces applied in a first stage, to the optical body by the ram of the forging press and, in a second stage, by the crystal powder, are non-uniform both in magnitude as well as in direction. The result is that the optical body may be deformed and forged to obtain a deformation ratio greater than 1.0 so as to obtain a fine-grain structure free of peripheral fissures and 'veiling'. Typically, a melt-grown essentially single macrocrystal of an ionic salt or of an optical oxide of aluminum or magnesium including certain optical mixed oxides such as bismuth germanium oxide, cadmium tungstate and lithium niobate, is hot press-forged while it is surrounded by a crystal powder of the same ionic salt or oxide. A polycrystalline extrudate of a melt-grown macrocrystal may also be hot press-forged in an analogous manner.

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First Claim