ESPI with structured illumination

In practical ESPI applications in industry, the object under investigation often has low reflectance. From theoretical analysis, it is shown here that the implementation of phase shifting techniques will result in a smaller fraction of acceptable measurements for a given level of tolerable phase error. The use of higher power lasers may solve this problem; but it is an expensive solution. In this work, structured lighting using diffractive optical elements is proposed as a cost-effective solution. The approach is particularly useful when the deformation phase has to be obtained from only selected areas on the object. A simple experiment conducted verifies the workability of this approach. (C) 2002 Published by Elsevier Science Ltd.