Analysis of error in measurement and resolution of electronic speckle photography in material testing

Causes and magnitude of error in measurement and resolution are investigated for electronic speckle photography (ESP), which is used like a strain gauge in material testing. For this purpose a model of the rough surface which allows the description of cross correlation of speckle images under the influence of material strain is developed. The process through which material strain leads to decorrelation of speckle images is shown. The error in measurement which is caused by defocused imaging and statistical errors in the displacement estimation of speckle images is investigated theoretically. The results are supported by simulations and experiments. Moreover the resolution of ESP can be improved through increased optical magnification as well as adjusted aperture. Resolutions which are usually considered to be accessible only to interferometric techniques are achieved. (author)