Speckle interferometry: refining the methods for taming disorder

In a two-beam interference experiment involving at least one speckle wave, intensity and phase are rapidly fluctuating distributions. There is no way to make a prediction of the evolution of the interference pattern aver distances greater than the correlation volume - as small as 3×3×100 μm3 for visible wavelengths and usual apertures. Most of the difficulties associated with a correct understanding and a good practice of speckle interferometry (SI) arise from this observation. It also explains why a technique simply ruled by the elementary two-beam interference or triangle formula raises nonetheless many problems. This contribution reviews some of the fundamentals of SI, mainly those concerned with the consequences of the random nature of the speckle phenomenon. It discusses what is thought to be the most interesting optical arrangements, modi operandi and phase extraction schemes, and finally presents selected applications. Constantly kept in mind is the idea to try to cope with the apparent disorder of the analyzed speckle distributions.