The basic principle of the white light speckle method for strain analysis is reviewed with a theoretical analysis of the recording and reconstruction processes of specklegrams including the effect of defocus. Ways to increase the sensitivity are proposed. The method's a-plicability to measuring inplane displacement, out-of-plane displacement, surface strain on a curved object, interior strain in a 3-D object, and large deformation is exemplified.
F. P. Chiang,
"Theory And Applications Of The White Light Speckle Method For Strain Analysis," Optical Engineering 21(4), 214570 (1 August 1982). https://doi.org/10.1117/12.7972953