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Glossary FAQ


13. Scheme of pulse transparent hologram recording

The great advantage of recording the holograms with the help of pulse laser consists in absence of problems connected with instability of fixing a photographic plate and an object. You can simply hold both a photographic plate and an object in your hands! It's possible to photograph people and animals, flowers and butterflies, soap bubbles and puffs of smoke. In essence there remains only one insignificant restriction on the object - its dimensions shouldn't exceed the photographic plate sizes. So you can imagine which freedom gains the holographists and painters working with three-dimensional images.
But payment for such freedom is a significant complication of equipment and technology. Use of pulse laser for recording holograms leads to a principal change both in optical lay-out of recording holograms and in their chemico-photographic treatment. The process of making a hologram by now includes two stages - recording a transmission master hologram and manufacture of a reflecting copy. Except for using complex and expensive pulse device the plant for copying a hologram on the basis of the He-Ne laser is also necessary (some companies manufacture pulse setups, which allow to record both transmission master-holograms and reflecting copies, but prices of these setups are very high).

By recording a transmission hologram both a reference and an object beams fall on the photographic plate from one side (see fig.). In essence it's one of the variants of the first holographic layout developed by Leith and Upatnieks immediately after invention of a laser. The laser beam 1 is divided into two beams by a semi-transparent mirror 2. The reference beam 5 is directed to the filter 4 by the mirror 3 and directly illuminates the photographic plate 8. The signal beam 6 is also directed by the mirror 3 passes through the spatial filter 4 and illuminates the object 7. For expansion of the signal beam opal glasses can be used instead of the spatial filter. The photographic plate registers the interference image created through interference between the reference light beam and the light reflected from the object.
After photo-chemical treatment of the photographic plate we obtain a transmisson hologram. If you illuminate such a hologram by the reference beam so looking through the hologram as through a glass plate you can see a three-dimensional image on the same place where the object was situated (see fig). Colour of the image is determined by the colour of laser radiation. And if by illumination with the help of a laser the transmitting hologram gives a faultless and sharp over the whole volume image, in the ordinary white light it restores only a diffuse achromatic image. For obtaining a high-quality image in white light the transmission hologram should be copied on the reflecting hologram.

The pulse holographic setup is shown on the photo. The pulse laser 1 with power supply units 2 and the layout of beams separation 3 is mounted on a separate support. The object is placed in the shooting cabin 4 - it's an important element of the setup. For increase of expressiveness of the holographic image the cabin should be equipped by various demountable backgrounds and additional means of illumination of objects - opaque glasses, mirrors, prisms, optical fibres etc. -->