Simple electronic speckle pattern shearing interferometer with a holographic grating as a shearing element

An optical set-up for electronic speckle pattern shearing interferometry (ESPSI) using a photopolymer diffractive optical element as a shearing element, is presented. A laser beam illuminates the object at an angle to the normal to the object surface. The holographic diffraction grating is placed in front of the object. The zero and the first order of diffraction form the image and the sheared image of the object. The images are imaged onto the CCD camera, whose optical axis coincides with the normal to the object surface. The field of view is limited only by the dimensions of the photopolymer plate. The photopolymer diffractive element is characterised by low level of light scatter and diffraction efficiency of 60%. The simplicity of the proposed new shearing interferometer is manifested by the extremely small number of components required - a coherent light source, a holographic optical element and a CCD camera.