 When lasers were first invented , laser speckle was considered to be a severe drawback in using lasers to illuminate objects , particularly in holographic imaging because of the grainy image produced . It was later realized that speckle patterns could carry information about the object 's surface deformations . Butters and <unk> developed the technique of speckle pattern interferometry in 1970 , and since then , speckle has been exploited in a variety of other applications . A photograph is made of the speckle pattern before deformation , and a second photograph is made of the speckle pattern after deformation . Digital subtraction of the two images results in a correlation fringe pattern , where the fringes represent lines of equal deformation . Short laser pulses in the nanosecond range can be used to capture very fast transient events . A phase problem exists : In the absence of other information , one cannot tell the difference between contour lines indicating a peak versus contour lines indicating a trough . To resolve the issue of phase ambiguity , <unk> may be combined with phase shifting methods . 
