ESPI based on spatial fringe analysis method using only two sheets of speckle patterns

Speckle interferometry is one of important deformation measurement methods for an object with a rough surface. A novel fringe analysis method using a new optical system, which uses a plane wave as the reference beam of the speckle interferometer, is proposed. When the optical system is employed in the fringe analysis, the deformation information and the bias components of the speckle patterns clearly are separated in frequency domain. Therefore, the deformation information can be readily extracted by using Fourier transform. In the fringe analysis processing, when the deformation information is extracted by Fourier transform, a pair of a real-part and an imaginary-part components concerning the information are given. The specklegrams are calculated by using such real- and imaginary-parts of the information. Consequentially, the fringe image is given as specklegram, and is spatially filtered. Sequentially, the phase map is calculated by using spatial fringe analysis method from the filtered specklegram. From experimental results, it is confirmed that the new method can analyze a deformation process with a convex and/or concave phase distribution in a high resolution power. It is also confirmed that the resolution power of the measurement by this method is much higher than 1/250 of the light source of the optical system.