In the holographic developing process there are several different chemicals and developers to choose from. In this experiment the whole holographic production process is tried out, and a basic procedure to use in the further work is established. The system is built up step by step from a simple holographic arrangement to an advanced holographic multi-stereogram arrangement.
Figure 7-1 Recording reflection hologram.
Figure 7-2 The position of the object relative to the film plate
The experimental set-up shown in figure 7-1 was made on the optical table.
Optical equipment used for the recordings :
He-Ne laser : Output power 12 mW. Wavelength 632.8 nm.
Spatial filters : Pinhole size 25 m. Microscope objectives 45x 0.65
Lenses : Diameter 100 mm. Focal length 175 mm.
Mirror : Flatness 
/10.
Filmplate : Type 8 E 75 HD. Resolution 5000 l / mm.
Filter : Transmission 20%.
Laserbeam distance: Object beam = 118 cm
Reference beam = 121 cm
Image 1:
Light power on the film : Object beam = 2.4 
W
Reference beam = 4.6 W
Light power ratio = 4.6 W / 2.4 W = 2:1
Exposure time : 40 seconds.
Result : It was possible to see the object in the hologram, but
the hologram was not bright. There were also observed dark shadows
or areas without any information. The hologram also had some
reflections on the image.
Comment : The poor brightness of the hologram is probably caused by too short exposure. Also, the reflections on the hologram reduce the hologram's quality.
Image 2 :
Light power on the film : Object beam = 2.4 W
Reference beam = 4.6 W
Light power ratio = 4.6 W / 2.4 W
2:1
Exposure time : 50 seconds.
Result : This image was better than image 1. There were no dark shadows, and the hologram has information all over the exposed area. The brightness of the hologram could be still better.
Comments : The exposure time is still too short.
Image 3 :
Light power on the film : Object beam = 2.4 W
Reference beam = 4.6 W
Light power ratio = 4.6 W / 2.4 W = 2:1
Exposure time : 60 seconds.
Result : This was the best image of the 3 holograms. But the image could still be brighter.
Comments : The problem with the brightness of the holograms is caused by the exposure time. It is very difficult to hold the optical equipment steady for more than 1 minute, without any vibrations.
Image 4 :
The purpose of the exposure is to get rid of the problem of reflections on the hologram. One of the problems with the holograms taken in the earlier stages in this experiment, was reflections from the lens. During the studying of the hologram it appears to be the lens in front of the filmplate which causes the problem. To solve this, the direction of the filmplate was changed.
The optical set-up for the exposure of this image is nearly the same as the set-up used earlier in this experiment. The alternation is shown in figure 7-3.
Figure 7-3 Location of optical equipment.
The object was changed to another one with lower depolarisation
degree. This was done to get more light reflection power from
the object in the same polarisation direction as the reference
beam. The filmplate is placed closer to the object to get even
more power from the object beam.
Light power on the film : Object beam = 2.3 W
Reference beam = 4.0 W
Light power ratio = 4.0 W / 2.3 W = 1.7:1
Exposure time : 65 seconds.
Result : This image was better than the holograms exposed on the
last set-up. There were no reflections from lens 2, because
the filmplate and the lens was not parallel.
Comments : To get a brighter hologram, a more stabile optical set-up is needed. It is completely impossible to get bright holograms without a multi stabile set-up when the exposure time is more than 1 minute. It is also very important that lens 2 and the filmplate are not parallel, because that gives rise to unwanted reflections.
Image 5 :
The purpose of this recording is to make a hologram with optimal
brightness and without any visible destructive noise. All the
optical components are placed as near as possible to the optical
table to reduce the possibility of any vibrations.
The alternation in the optical set-up is shown in figure 7-4.
Figure 7-4 Location of optical set-up
The optical equipment used for this exposure is the same as in
the earlier experiment.
Light power on the film : Object beam = 1.0 W
Reference beam = 1.6 W
Light power ratio = 1.6 W / 1.0 W = 1.6:1
Exposure time : 80 seconds.
Result : The hologram is very clear and bright.
Comments: This reflection hologram was very good. This is the
desired quality of holograms in the final product.
The optical table and the optical equipment are good
enough to produce first class holograms.
Optical equipment used for the recordings :
He-Ne laser : Output power 12 mW. Wavelength 632.8 nm.
Spatial filters : Pinhole size 25 m. Microscope objectives 45 x 0.65
Lenses : Diameter 100 mm. Focal length 175 mm.
Mirror : Flatness /10.
Filmplate : Type 8 E 75 HD. Resolution 5000 l / mm.
Figure 7-5 Optical set-up for the recording of image 1
The result of this experiment will of course not be a 3 dimensional holographic image, since the picture, shown on figure 7-6, on the transparency film is only in 2 dimensions.
Figure 7-6 Picture of the cube used in the experiment.
Image 1 :
The laser beam distance : Object beam = 167 cm.
Reference beam = 166 cm.
Laser power at the film : Object beam = 3.5 W.
Reference beam = 6.2 W.
Light power ratio = 6.2 W / 3.5 W = 1.8 :1
Exposure time = 40 seconds.
Result : The hologram was very bad. There was a dark circular area without any information in the centre of the filmplate, shown in figure 7-7.
Figure 7-7 Reconstruction of the hologram.
Comments : The dark area on the hologram is caused by reflections from the lens (placed on the reference beam) that are parallel to the filmplate. It is very important that the lenses are not parallel to the filmplate.
Image 2 :
This set-up is a further extension of the recording of image 1.
The main difference between these two exposures is that the lens
(on the reference beam) is not parallel to the filmplate.
Figure 7-8 Set-up for the recording of image 2.
The laser beam distance : Object beam = 148 cm.
Reference beam = 147 cm.
Laser power at the film : Object beam = 3.5 W.
Reference beam = 7.5 W.
Light power ratio = 7.5 W / 3.5 W 2.1 :1
Exposure time = 40 seconds.
Result : The quality of the hologram was not satisfactory. It
was possible to see the image on the hologram, but the contrast
was bad.
Comments : The bad quality of the hologram is probably caused
by reflections from the optical equipment.
Image 3 :
The angle between the reference beam and the filmplate is changed from 53o (for image 1) to 55o. This is done to prevent the reference beam from striking the ground glass, and causing reflections which disturb the recording process.
Figure 7-9 Location of optical set-up for image 3.
Light power at the film : Object beam = 3.5 W
Reference Beam = 7.5 W
Light power ratio = 7.5 W / 3.5 W = 2.1 :1
Exposure time = 60 seconds.
Result : The hologram's image was without any reflections, and
the brightness was good.
Comments : It was very important to get good results with this experiment, as this method is the basic principle for further experiments. It is also satisfactory that the optical equipment is stable for an exposure of 60 seconds.
Image 4 :
The idea behind this exposure is to see the purpose of the ground glass. We know that the ground glass spreads the information from the picture (in this case a transparent 2-D draw) in all directions. This must be done to get the same diffusion which we get when light is reflected from an object.
Figure 7-10 Location of optical set-up for exposure 4.
Figure 7-10 shows the changes in the optical set-up used in the
recording of image 3. The difference between this and the earlier
set-ups is the ground glass. The ground glass is not used in this
experiment.
Laser beam distance : Object beam = 148 cm
Reference beam = 147 cm
Laser power on the film : Object beam = 3.5 W.
Reference beam = 6.0 W.
Light power ratio = 6.0 W / 3.5 W = 1.7 :1
Exposure time = 50 seconds.
Result : The hologram is unusable because the picture is exposed
directly on the filmplate like in a photograph.
Comments : To get the picture exposed on the filmplate as a hologram, we have to use ground glass in this type of set-up. This is because each point of the film contains information from the whole picture.
Figure 7-11 Set-up for experiment 3.
A polarizer is placed close to the filmplate, so that the light from the object beam is polarised in the vertical direction when it illuminates the film. The polarizer does not cover the whole filmplate, because one should be able to see the difference between the area with polarizer and the area without.
Figure 7-12 The vertical polarizer
Figure 7-12 shows the location and the shaping of the polarizing filter. The film is divided into 4 parts where 2 are with polarizing filter and 2 without. The area behind the polarizing filter is totally polarized in the vertical direction. The light is 80 present polarized in the vertical direction where no polarizing filter is used.
The picture which is fastened to the ground glass is shown in figure 7-6.
Optical equipment used for the recordings :
He-Ne laser : Output power 12 mW. Wavelength 632.8 nm.
Spatial filters : Pinhole size 25 m. Microscope objectives 45 x 0.65
Lenses : Diameter 100 mm. Focal length 175 mm.
Mirror : Flatness / 10.
Filmplate : Type 8 E 75 HD. Resolution 5000 l / mm.
Laser beam distance : Object beam = 148 cm
Reference beam = 147 cm
Image 1 :
Light power on the film : Object beam = 3,5 W to 5.0 W
Reference beam = 7.0 W
Light power ratio = 1.4 : 1 to 2:1
Exposure time 80 seconds.
Result : The quality of the hologram was very good. The image was bright all over the area without any visible loss of information.
Comments : The depolarizing effect of the object beam does not lead to any quality reduction of the hologram. The depolarized light from the object which illuminates the filmplate will not interfere with the reference beam, when this is totally polarized in this vertical direction. Of course, the depolarized light will also
blacken the film, but this is not a problem since the film goes through a bleaching process after it has been developed. When we are looking at the hologram can we see the image with and without polarizer, because the
polarizer is also recorded in the hologram. The area of the hologram where the polarizer is cover the holographic image has the same quality as the area without polarizer.
Image 2 :
This optical set-up is the same as used for the exposure of image 1, but this hologram is made without using the polarizing filter.
Figure 7-13 Picture of a BCC crystal structure.
The picture in figure 7-13 is copied onto a transparency film
and replaced with the image used in the earlier experiments. The
picture of the BCC crystal absorbs much more light than the picture
which had been used earlier.
Light power on the film : Object beam = 3.7 W
Reference beam = 6.9 W
Light power ratio = 6.9W / 3.7 W 1.9 :1
Exposure time = 112 seconds.
Result : The quality of the hologram was very good. The brightness of the image was very satisfactory.
Figure 7-14 Picture of the hologram.
Comments : It appears that the optical equipment and the practical holographic recording procedure works well for this type of experiment.
