Report of the nations: Belgium
Belgium is probably the most productive holographic nation, insofar the production of silver halide material is concerned, and silver halide is still the workhorse for a very large number of holographic applications, both in display and technical fields.
Wellspring with dying leaves
As was already noted and repeated to saturation by a number of prominents, big is beautiful. Therefore it was tried to make a monumental (biggest in the world?) hologram mosaic, that, combined with properly aligned mirrors, would provide the impression of infinity to naive onlookers. Due to the cost of such a project and the financial situation of Belgian universities, a maquette was first made and presented to a number of potential sponsors. After a couple of years, we were lucky enough to be able to produce the real thing, i.e. one quarter of an octogonal fountain pit of about 3 by 3 metres (10x10 feet) surrounded by stairs. The walls were provided with mirrors, two of them, in front of the spectators, providing a kaleidoscopic effect, three smaller ones giving rise to a repetitive reflection. The bottom of the well was a Denisyuk hologram mosaic of leaves; by some optical tricks, it was tried to simulate the effect of shivering water surfaces. The evolution of the proj ect with time, the practical problems involved, the final realisation, the advantage and the shortcomings of the presentation during a technology fair will be discussed.
Use of Reflection Holograms in Holographic Interferometry and Speckle Correlation for Measurement of Surface-displacement
When a special case of a Denisyuk set-up [1] is used for double-exposure holographic interferometry, namely, with the photographic plate fixed to one point of the object under study and plane illumination through the plate, some interesting advantages can be obtained. The stability requirements are drastically reduced (a general translation and a rotation around an axis parallel to the illumination direction can be allowed); the optical set-up is very simple; white-light reconstruction can be used. For the determination of in-plane displacement patterns, one can either use fringe-order subtraction between two symmetrical off-axis views (eventually Moire subtraction), or use speckle correlation techniques. The most important advantage is that Cartesian components of displacements can be determined with complete object motion compensation by combining holographic and speckling techniques. Some practical applications of the method and its drawbacks are presented.