Introduction

Abstract

In the year 1948, D. Gabor described “a new microscopic principle” laying the foundation for the reconstruction of the image of an object from a diffraction pattern produced by that object. Because this technique made it possible to record not only the amplitude but also the phase of a light wave, its inventor named it “holography” (from òλoς = entire and γραϕειν = to write). At that time however, two obstacles had to be overcome: on the one hand, no sufficiently monochromatic and coherent light source was available and, on the other hand, observation of the image was hindered by overlapping of the wave fields at the reconstruction. In 1962, E. N. Leith and J. Upatnieks remedied this situation by using a laser beam (i.e. Light Amplification by Stimulated Emission of Radiation) as a light source and by providing the object wave and the reference background with two different directions. Since then, holography rapidly developed and found many an application in various domains of science. Three years later, the insight that a holographically produced wave field could be brought to interfere with another wave field, whether holographically produced or not, particularly fascinated several researchers.