Holographic Interferometry

The one of the important testing process is non destructive testing of specimen which basically depends upon interferometric methods. The nature of holographic process to give objective analysis of a specimen when illuminated with a reconstruction wave allows us to have interference leading to a method called double exposure holographic interferometry. This uses the photographic process between the object wave and a reference wave of a specimen which is under stress alternatively to create a hologram. The holograms so created give us two object waves when illuminated with reconstructive wave, the first one for an unstressed object and the other one for the stressed object. When these are overlapped again they gives us the interference pattern leading to the information about the qualitative and quantitative stress distribution. Since interference is involved in the whole process the slightest variation in the stress distribution can be analyzed.There is another type of holography known as variant holography which gives us what is known as real time interferometry in which a hologram is formed of an unstrained object and the image produced by the hologram is superimposed on the reconstructed object of a strained specimen. If the object undergoes any strain, fringes will be formed and this can be studied as function of time. Such type of studies is used in study of vibrating objects like musical instruments etc.