Deformation measurements of specularly reflecting objects using holographic interferometry with diffuse illumination

It is demonstrated that, by using diffuse object illumination, deformation measurements with holographic interferometry can be performed on a specularly reflecting object without the use of any additional coating of the object surface. An analytical expression for the secondary fringe formation is found, and the system is demonstrated only to be sensitive to deformations along the surface normal. A method for carrying out topographic measurements on specularly reflecting surfaces is suggested. The fringe visibility is studied for a rigid rotation of the object by using matrix methods. It is found that maximum fringe visibility is obtained if the recording camera is focused on the surface of the object.