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The
recording procedure of reflective volumetric holograms
is another. The idea of making of such holograms
belongs to Uri N. Denisyuk.
Therefore holograms of this type are known under
the name of their founder.
The reference and
object light beams are formed with the help of a semi-transparent mirror and directed by a
mirror on a plate from two opposite sides. The object wave shines a photographic plate on
the part of an emulsion layer, reference wave - on the part of a glass substrate. The
Bragg's planes in such requirements of recording scheme almost parallel planes of a
photoplate. Thus, the thickness of a photolayer may be rather small.
On the recording scheme
the object wave is formed from the transmission hologram. I.e. in the beginning usual
transmission holograms are made by the technology, described above, and then make in a
copying mode the Denisyuk's holograms from these holograms (which are termed the master
holograms) .
The basic property of
the reflective holograms is an opportunity of reconstruction of the image with the help of
a source of white light, for example, incandescent bulb or the Sun. The important property
is the colour selectivity of such hologram. It means, that at the image reconstruction by
a white light, it will be restored in colour, that was used during hologram recording. For
example, if ruby laser (red light) was used for recording procedure, the restored image of
the object will be red.
According to property
of colour selectivity it is possible to manufacture colour hologram of the object, exactly
reproducing its natural colour. For this purpose it is necessary to mix three colours at
the hologram recording: red, green and blue or to shine consistently a photoplate by these
colours. But, technology of the colour holograms manufacturing is in an experimental stage
and some more efforts and experiments will be required. It is remarkable, that a lot of
people, visitors of exhibitions of the holograms, usually say, that they can see the
colour volumetric images!
Additional
information about physical principles of holography you can read in articles of our "Technology" and "Files"
sections.
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