Digital holographic interferometry in a disturbed environment

Abstract: Digital holographic interferometry is an optical measurement technique that is capable of measuring the movement/deformation of an object surface with extremely high accuracy, spatial resolution and temporal resolution. But, because it is very sensitive to disturbances, it is mostly used in well controlled laboratory environments. An exciting new application of the method could be for process supervision in the manufacturing industry. But before it can be used in such an environment it must be made more insensitive to disturbances. The work in this thesis deals with post processing of data from holographic interferometry measurements to reduce the effects of mechanical vibrations and random refractive index fluctuations in the surrounding air. The first approach of using a purely temporal interference filter was successful in reducing the noise due to vibrations, but the noise from the air disturbance was only reduced over a very limited spatial region. A more complete spatio-temporal filter that is not of the interference type requires that the spatio-temporal statistics of the noise from the air can be measured. Therefore the rest of the work is devoted to this problem. The method developed is applied to the relatively simple case of locally homogenous/isotropic refractive index fluctuations generated in a small wind tunnel. There is a simple theory for these types of fluctuations for which the method was successfully verified.