Construction and operation of a simple electronic speckle pattern interferometer and its use in measuring microscopic deformations

The construction and operation of a simple electronic speckle pattern interferometer (ESPI) is described. The underlying theory behind the operation of the interferometer, which is sensitive to out-of-plane displacements, is given. The interferometer uses a commercial digital still camera for image acquisition and a personal computer for image storage and analysis. The interferometer was used to measure microscopic deformations of a steel plate caused by small loads. The results were found to be in good agreement with the predictions of the elastic theory. Various possible applications of the interferometer are mentioned.