ALarge-shearing block prism in electronic speckle pattern interferometry

A large-shearing block prism is designed, which can be used in electronic speckle pattern interferometry (ESPI). A wedge is made of a beam splitter cube on one of its surface. The oblique plane and one of its adjacent surfaces of the block are coated by reflection enhancing film. And other two surfaces are coated by anti-reflection films. When a normal incidence beam arrives at one of the reflect-reducing coating surfaces, the beam is split into two after inner beam-splitter. The two outgoing beams can be separated from each other when they are reflected by a parallel reflector and a tilted reflector respectively. If the large-shearing block prism is placed in front of the lens of a CCD camera, an object can be imaged into two shearing images and two adjacent objects can be imaged at same place on image plane. The shearing amount of the image is determined by the angle of the wedge. A large-shearing electronic speckle pattern interferometry (ESPI) can be realized by using the block prism if the shearing amount is sufficient. The angle can be selected from 1 degree to 10 degree based on the size of test specimen and the object distance. Carrier modulation experiments using a centrally loaded clamped circular plate are completed. The experimental results prove that the large-shearing block prism can be used in ESPI and the displacement fields can be obtained effectively.