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14. VRP photoplates
VRP
photographic plates ("Slavich" production)
are used for recording of pulse transmission holograms.
These plates are sensitized to green light. Although
these photographic plates were originally developed
for photo-lithography, they are also suitable for
recording holograms. Moreover stability of properties
of the emulsion layer of photographic plates VRP
is much higher than in the case of purely "holographic"
plates (PFG series). They can be stored several
years outside refrigerators without deterioration
of their photographic properties.
Thickness of the emulsion layer of the photographic
plates VRP is 5 micron. From the side of the glass
substrate they are covered by a transparent anti-aureole
red color layer which immediately discolors in a
developer.
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Grains of silver bromide in the emulsion layer of
the photographic plates VRP have the dimensions
of about 40 nm (see figures). These dimensions are
several times greater than the grain dimensions
in the photographic plates PFG-03m. So, sensitivity
of VRP plates is several times higher (for phase
holograms) - about 75 mcJ/sq.cm (see fig.). On the
other hand resolution of the VRP plates doesn't
exceed 3000 lines/mm because of big sizes of the
silver bromide grains. Because of this fact the
process of recording reflection holograms on VRP
plates is connected with certain difficulties. It's
practically impossible to obtain bright Denisyuk
holograms on the VRP plates, but by copying reflection
holograms from transmission master holograms it's
possible to get copies of satisfactory quality on
the VRP plates by a fine optimization of the conditions
of exposition and chemical treatment. For recording
reflecting holograms it's necessary to use photographic
plates without a anti-aureole layer. They are marked
as VRP-M (see fig. below).
Besides
VRP photographic plates, "Slavich" manufactures
cheaper plates FPR (see right fig.). They are also
sensitized for green color, and they have the same
sensitivity and resolution as the VRP plates, but
they have some worse mechanical properties - strength
and temperature of deformation of the emulsion layer.
These characteristics have no critical importance
for hologram recording, so using of the FPR plates
is preferable. -->
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