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Technology of hologram recording
by pulse neodimum laser
There is description of
hologram recording on VR-P photoplates ("Slavich production) by pulse neodimum laser.
Comprehensive information is given in [1].
In accordance with the
failure of the reciprocity law [2], the sensitivity of
holographic photoplates is significantly reduced at very short exposures.This directly
influences the recording of pulsed holograms by Nd lasers which have a pulse duration of
around 20 ns. Consequently it becomes necessary to increase the energy of the pulse or to
use non-optimum development with an associated increase of the noise in the reconstructed
image of the hologram. To eliminate this undesirable phenomenon it is possible to use an
effect known in photography as latensification [2,3]. This
effect consists of strengthening the latent image directly after recording the hologram by
a long exposure to weak incoherent light. This leads to an increase of size of the centres
of the latent image up to sizes characteristic of a normal exposure. It is remarkable that
the influence of such weak light on a non-exposed photoplate does not result in the
occurrence of any appreciable density after development.
For the purposes of
latensification a photographic light source with a frosted lamp of 40 W with green filter
was used. The distance between this light source and the hologram was 80 cm. The
photochemical processing sequence that we used is given below:
1. Development in VR-P developer 2 min.
2. Washing 5 min.
3. Fixation 10 min.
4. Washing 5 min.
5. Bleaching up to full transparency.
6. Washing 10 min.
7. Drying in 50% , 80% , 100% ethanol 2 min. |
For the
reduction of noise in the reconstructed image the proprietary VR-P developer was modified.
The amount of sodium sulphite in it was reduced from 140 g/l down to 50 g/l. The recipes
of the modified developer and bleach are given below:
VR-P Developer |
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Bleach |
Metol 6 g
Sodium sulphite 50 g
Hyroquinone 20 g
Potassium metaborate 112 g
Potassium hydroxide 17,42 g
Water 1 l |
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Ferric nitrate 150 g
Potassium bromide 30 g
Water 1 lBefore use dilute 1:3 |
The
optimum time of latensification was found as follows. A photoplate was cut into some small
pieces. All the pieces except one were placed at a given distance from the light source
and were illuminated for different times. The non-illuminated piece is necessary for an
estimation of the haze of the photoplate. Then all pieces were developed in one bath and
fixed. The optimum time of latensification was determined as the time required for the
density of an exposed photoplate to just exceed the density of the haze of the control
plate.
Optimum latensification
gives an increase in the opacity of the recorded hologram of more than ten times (D=1). In
this sense it is possible to speak about a ten times increase in the sensitivity of the
VR-P photoplate. A visual estimation of the quality of the reconstructed image of the
bleached holograms shows a significant.-->
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