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25 holography lessons

Glossary FAQ


8. Hologram recording

Well, everything is ready to record a hologram: holographic system was installed, photoplates were prepared and exposure time was measured. If a size of photoplate does not correspond to a size of a hologram, you should cut a photoplate of the necessary size, e.g. 9x12cm. Beforehand you have to make a sketch on a white paper and purchase a glass-cutter.
Quality of cutting depends greatly on a glass-cutter. It is better to use a diamond glass-cutter since it produces a flatter cut line and less glass splinters. Try to cut a piece of usual glass beforehand till your cutting becomes stable and qualitative, because at the weak light your operations must be very neat.

Cut a standard photoplate of a hologram size using a glass-cutter and put it on three supports with its emulsion layer below (See lesson 6). Cover the front edge with a piece of black paper. It is necessary to prevent penetration of a reference beam onto the photoplate edge and its reflection inside the glass that may cause a series of parallel dark strips in the image. If a shadow of black paper piece spreads over the object of shooting or the background, you should increase the size of photoplate, e.g. up to 9x14 cm (See photo). You can see on the photo that shadow spreads over the upper part of the white background. It is possible to cut an extra piece of the photoplate when a hologram is ready.
Cut a sheet of red or black paper of the hologram size and put it onto the glass plate. Check homogeneity of lighting, if it is necessary adjust the beam position. Cover the beam with a piece of black paper in such a way it can be easily removed before exposure starts.
Switch the white light off and switch the weak green light on. The photoplates are not sensitive to it. Put your rubber gloves on. Open a box with photoplates, take out one of them and put it on the template, emulsion layer should be below. It is easy to define where the emulsion layer is. Breath on the photoplate surface. If it is misted, it is glass. If it is not misted, it is an emulsion layer (gelatin absorbs moisture from the air). You should cut the photoplate only on the glass side. After each cutting procedure shake off the template to get rid of splinters otherwise you may scratch the emulsion layer. Cut photoplates directly before their exposure. Cut photoplates directly before their exposure. Contacts of photoplates and paper decrease shelf life of photoplates. Because of that at the factory plates are always packed by pairs through the edge seals with the emulsion layer inwards.

Take a photoplate and look at the weak green light through it. If you notice specks of dust or glass splinters on the photoplate surface, remove them very carefully with a soft brush. If glass splinters are not removed with a brush, they may be removed with a sharp knife or a razor blade but only on the glass side!
Check the photoplate and put it carefully onto the supports and shut its front edge with a piece of black paper. Wait for a minute. It is necessary to eliminate mechanical and heat stresses in the photoplate before it is exposed. These stresses may cause micro shifts of the plate and degradation of the hologram quality. According to calculations, shift of interference pattern should not be more than 0.005 mkm. Stabilization time increases when a photoplate size increases. Stabilization time should be at least 5 min for a hologram of 18x24 cm.
Open the laser beam and expose the photoplate. Try to be not very close to the photoplate since your movements may affect the photoplate position. Ideally it is possible to make a camera shutter with remote control and expose a hologram from the next room. So that influence of mechanical and heat vibrations of air on the photoplate during its exposure will be completely removed.
If the hologram brightness is not very good, you must check if the table of recording damp out vibrations well. (See recommendations of lesson 6).
After exposure, put the photoplate in the box with its emulsion layer upwards. -->