::Scheme of Denisyuk's hologram recording

The scheme got its name from the famous Russian scientist - Yury Nikolaevich Denisyuk, who invented the procedure of reflection hologram recording on transparent photographic plates in the beginning of the seventies. Before that holograms were recorded according to Leith-Upatnieks method and a laser was necessary for their observing. Denisyuk proposed to expose the plate and the object with the same laser beam to see holograms in the usual white light. It was necessary to develop special photo plates, which had to be transparent and have very high resolution. The problem was successfully solved.

First figure shows a scheme of Denisyuk's hologram recording and the second one demonstrates a photo of a real setup. Narrow light beam 2 from the laser 1 is directed by the mirror 3 to spatial filter 4, which expands the beam up to the necessary size and simultaneously improves its homogeneity. Expanded beam 5 exposes photoplate 6 and the object 7, which is fixed on a rigid base 8. Laser light is reflected from the object to the photoplate from the reverse side. Two beams meet each other in the photoplate's plane: the first beam goes from the laser and it is called a "reference beam" and the second one, which goes from the object, is called a "signal beam". These beams create an interference pattern, which is registered on the photo plate. An interference pattern represents the smallest differences of a light intensity with the period less than 1micron. A complete immobility of the object and the photo plate during exposing is necessary to register such a fine pattern. Therefore soft objects and living objects, for instance, animals, cannot be recorded in the scheme with the continuous-wave laser.