Figure 1.

Summary of the working principle of ESPSI. (a) Spatially and temporally coherent light is used to illuminate the surface of the object, if the surface of the object is rough (height variations >λ/4) the light scattered from the object has a random phase, constructive and destructive interference of this light results in a speckle pattern, which is captured on a charge-coupled device (CCD) chip; (b) the object beam is split into two parts via a beam splitter—one of these beams is transformed laterally and the beams are combined on the surface of the CCD chip. A unique speckle pattern is captured from the object in its reference state and stored, the object is then loaded and a second speckle pattern in captured, phase stepping is used during data capture so quantitative data can be extracted; (c) the loaded speckle phase data are subtracted from the reference speckle phase data in real time resulting in subtraction fringes. A wrapped phase map is generated from the phase stepped data, these wrapped data are then unwrapped to give the absolute phase change due to deformation (Δφ_def) for each pixel in the image plane.