Electronic speckle pattern shearing interferometry using photopolymer diffractive optical elements for vibration measurements

Electronic speckle pattern shearing interferometry (ESPSI) is superior to Electronic speckle pattern interferometry (ESPI) when strain distribution, arising from object deformation or vibration, need to be measured. This is because shearography provides data directly related to the spatial derivatives of the displacement. Further development of ESPSI systems could be beneficial for wider application to the measurement of mechanical characteristics of vibrating objects. Two electronic speckle pattern shearing interferometers (ESPSI) suitable for vibration measurements are presented. In both ESPSI systems photopolymer holographic gratings are used to shear the images and to control the size of the shear. The holographic gratings are recorded using an acrylamide-based photopolymer material. Since the polymerisation process occurs during recording, the holograms are produced without any development or processing. The ESPSI systems with photopolymer holographic gratings are simple and compact. Introducing photopolymer holographic gratings in ESPSI gives the advantage of using high aperture optical elements at relatively low cost. It is demonstrated that both ESPSI system can be used for vibration measurements. The results obtained are promising for future applications of the systems for modal analysis.