[Diffraction halo]

Diffraction halo produced by a coarse speckle pattern transparency placed in the focal plane of a helium-neon laser, photographed by I M Andrews and M H Dossett of IBM United Kingdom Laboratories, Hursly Park. This photograph was taken during the setting up of equipment for analysing speckle pattern photographs, during measurements of the inplane strain of a component. This successful technique can measure displacements down to a fraction of 0'001 in, without any contact being made with the object