Figure 12-6 Experimental set-up for reflection hologram recording.
The LCD and the shutter is connected to computer, where the LCD is connected in parallel to the computer screen. The computer image used in this experiment is the same as used in experiment 1, shown in figure 12-2. The distance between the LCD and the film is 11 cm, and the ground glass is fastened to the display.
Optical equipment used for the recordings :
He-Ne laser : Output power 24 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 5000l / mm.
Filter : Transmission 50 %.
LCD : Transparency LCD
Laser beam distance : Object beam = 199 cm.
Reference beam = 199 cm.
Image 1 :
Light power on the film : Object beam = 0.8 W.
Reference beam = 1.8 W.
Light power ratio : 1.8 W / 0.8 W
2.3 :1
Exposure time : 100 seconds.
Result : The brightness of the hologram could have been better.
Comments : It seems that the hologram had been unevenly illuminated
during the exposure.
This can be seen from the reconstruction of the hologram,
where the brightness is not even over the whole area
of the filmplate.
Image 2 :
Before this exposure the spatial filter was adjusted, and the
reference beam illuminates the film uniformly over the whole area.
Light power on the film : Object beam = 0.8 W.
Reference beam = 2.0 W.
Light power ratio = 2.0 W / 0.8 W = 2.5:1
Exposure time = 100 second.
Result : The quality and the brightness of the hologram were very
good.
Comments : This type of set-up ( optical set-up in two levels) is very flexible, and it is possible to make good transmission and reflection holograms. Therefore this 2 level set-up will be preferred in further experiments.
In this experiment the aim is to produce transmission holograms from computer pictures. In the earlier experiments, holograms were made from one computer picture only. When only one picture is used, the result will only be a 2-dimensional holographic image of the computer picture.
In this experiment the purpose is to make 3-dimensional hologram
from 70 different pictures. These pictures are drawn with AutoCAD,
where the drawn object is turned over on the screen, and make
it possible to see the image from the left, front and from the
right side. These 70 pictures are exposed on 70 different area
of the filmplate with the help of the holographic printer.
Figure 12-7 Experimental set-up for recording transmission holograms with the use of a 3-D printer.
The computer screen is connected in parallel with the transparent LCD, and is illuminated by the object beam.
Figure 12-8 Location of optical equipment.
The picture of the object is made by turning the perspective AutoCAD drawing from right to left or in the opposite direction. For every degree the picture is turned we have a new image. The total visible angle is about 70 (from the first to the last picture).
Figure 12-9 shows an example of the picture used in the process
(here only 3 different pictures are shown).
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Figure 12-9 Pictures used in the recording process.
Every one of the 70 pictures is exposed on different areas of the filmplate.
The printer that moves the filmplate to the right position is described in section 9.1 The holographic printer .
The picture exposed onto the film must be the right image, exposed on the right area of the filmplate. The filmplate is illuminated in vertical columns which can be adjusted from 0 mm to 5 mm width.
Figure 12-10 Exposures of the filmplate.
The first computer picture is exposed in the first position of the filmplate, and the second picture is exposed in the second position and so on. Totally 70 different pictures are exposed onto the filmplate in the 70 different vertical columns.
During the reconstruction of the hologram we can see the image from the left side when we look at the hologram from the left side. If we look at the hologram from the front, we will see the image from the front, and of course if we look at the hologram at the right side we will see the image from the right side. Holograms produced in this method will give us a hologram with the image in 3 dimensions (3-D) image. This means that we get a hologram made from 70 different holograms, which we perceive as one hologram with a 3-D image.
Optical equipment used for the recordings :
He-Ne laser : Output power 24 mW. Wavelength 632.8 nm.
Spatial filters : Pinhole size 10 m. Microscope objectives 45
x 0.65
Lenses : Diameter 100 mm. Focal length 175 mm.
Mirrors : Flatness / 10.
Filmplate : Type 10 E 75. Resolution 3000 l / mm.
Filter : Transmission 20 % .
LCD : Transparency LCD
Laser beam distance : Object beam = 155 cm.
Reference beam = 155 cm.
The ground glass is changed to ground paper to get a better spreading of light from the LCD. The disadvantage with the use of ground paper is its bad transparency. This means there will be a greater loss of light power of the object beam than there would have been with the use of the ground glass.
Image 1 :
To obtain the maximum light power on the filmplate during the
exposure, the polarisation direction of the laser was turned so
that the LCD could transmit the maximum possible light power.
Light power on the film : Object beam = 0.05 W.
Reference beam = 0.10 W.
Light power ratio = 0.10 W / 0.05 W = 2:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.75 mm.
The slit width is chosen a to be slightly wider than the distance
the filmplate moves, in order to overlap and reduce the effect
of vertical lines.
Settle time = 5 seconds.
Exposure time = 30 seconds.
Result : The hologram is good, but the lowest part of the hologram
is brighter than the top. The vertical lines on the hologram
are very distinct.
Comments : The lowest part of the film had the weakest reference
beam. This means that the ratio between the reference
beam and the object beam should be less than 2:1.
Image 2 :
The optical set-up for image 2 is the same as used in the recording process of image 1.
The reference and the object beams were adjusted to obtain a more
uniform illumination of the film.
Light power on the film : Object beam = 0.02 W.
Reference beam = 0.02 W.
Light power ratio = 0.02 W / 0.02 W = 1:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.75 mm.
Settle time = 5 seconds.
Exposure time = 30 seconds.
Result : The hologram is good and the brightness is better than
for image 1. The vertical lines on the hologram are still very
distinct.
Comments : The slit width or the movement of the filmplate must be changed to reduce the vertical lines in the hologram.
Image 3 :
The optical set-up for image 3 is the same as that used earlier
in experiment 4.
Light power on the film : Object beam = 0.02 W.
Reference beam = 0.02 W.
Light power ratio = 0.02 W / 0.02 W = 1:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.64 mm.
The distance the filmplate is to be moved between the exposures
is reduced to get a bigger overlap.
Settle time = 5 seconds.
Exposure time = 15 seconds.
The exposure time is reduced to the half of that used for the
earlier image recordings in this experiment. The purpose of this
new exposure time is to try to reduce the time of the recording
process and also to reduce the possibility of instabilities. The
exposure time must not be to short, because if the hologram is
under-exposed the brightness will be bad.
Result : The hologram is good and the brightness is the best so
far in this experiment. The vertical lines from the slit are
more pronounced than ever.
Comments : In this experiment the movement of the filmplate was reduced, and it brought a larger overlap. It appears that if the overlap is too large, the vertical stripes from the slit become more visible. The exposure time seems to be suitable, since the brightness of the hologram is good.
Image 4 :
The optical set-up for image 4 is the same as that used earlier
in experiment 4.
Light power on the film : Object beam = 0.02 W.
Reference beam = 0.02 W.
Light power ratio = 0.02 W / 0.02 W = 1:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.80 mm.
The distance the filmplate is to be moved between the exposures
is increased to give a smaller overlap.
Settle time = 5 seconds.
Exposure time = 17 seconds.
The exposure time is increased by 2 seconds in order to get a
brighter hologram.
Result : The hologram is good and the vertical lines are minimal.
Comments : It would be difficult to use the holograms produced in this process as master holograms for a recording process of 2-step reflection holograms. This is because the size of the real image is too big.
Image 5 :
To solve the problem of too large real image, and obtain holograms which can be used as master holograms in a 2-step reflection hologram recording method, the reference beam and object beam were adjusted to be parallel. Has this anything to do with the size of the real image ?
The optical set-up for image 5 is the same as used earlier in experiment 4.
Light power on the film : Object beam = 0.02 W.
Reference beam = 0.02 W.
Light power ratio = 0.02 W / 0.02 W = 1:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.85 mm
The distance the filmplate is to be moved between the exposures
is increased to give a smaller overlap.
Settle time = 5 seconds.
Exposure time = 17 seconds.
Result : The quality of the hologram is good, but the size of
the real image is still too big. The vertical lines from the
slit are smaller than ever.
Comments : The change from not parallel to parallel reference and object beams makes no alteration in the size of the real image.
Image 6 :
To get a smaller real image on the hologram, the LCD is placed closer to the filmplate. Because of the size of the LCD's cover, it is impossible to get LCD nearer the film without blocking the reference beam. This problem is solved by removing the cover from the LCD.
Figure 12-11 Location of optical equipment.
The optical set-up for image 6 is the same as used earlier in experiment 4.
Light power on the film : Object beam = 0.04 W.
Reference beam = 0.08 W.
Light power ratio = 0.08 W / 0.04 W = 2:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.85 mm.
Settle time = 5 seconds.
Exposure time = 15 seconds.
The exposure time is reduced by 2 seconds because the light power
in the object and the reference beams have increased.
Result : The hologram is good and the real image is smaller than
the earlier images in this experiment.
Comments : The size of the real image depends on the distance between the LCD and the film.
Image 7 :
The holographic film needs more light power to reduce the exposure
time. Therefore the ground paper was changed to ground glass which
is more transparent. The purpose of this exposure is to test whether
the quality of the ground glass is good enough for use in holography.
Will the ground glass spread the light from the LCD well enough,
and is the transparency of the ground glass much better than the
transparency of the ground paper ?
The optical set-up for image 7 is the same that used earlier in experiment 4.
Light power on the film : Object beam = 0.25 W.
Reference beam = 0.45 W.
Light power ratio = 0.45 W / 0.25 W = 1.8:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.85 mm.
Settle time = 5 seconds.
Exposure time = 10 seconds.
The exposure time is reduced by 5 seconds because the light power
of the object beam and the reference beam have increased.
Result : The quality of the hologram is bad because it is strongly
over-exposed.
Comments : The ground glass transmits over 10 times so much light
as the ground paper. In image recording is it impossible
to draw any conclusions about the quality of the ground
glass.
By correcting the position of some of the optical components, it is possible to place the LCD nearer the film. This is done to reduce the size of the real image, and it will be possible to use it as a master transmission hologram.
The LCD changes the polarisation direction by 20. To correct this a half-wave plate 17 is mounted on the reference beam on the optical set-up.
Figure 12-12 Location of optical equipment.
Optical equipment used for the recordings :
He-Ne laser : Output power 24 mW. Wavelength 632.8 nm.
Spatial filters : Pinhole size 10 m. Microscope objectives 45
x 0.65
Lenses : Diameter 100 mm. Focal length 175 mm.
Mirror : Flatness / 10.
Filmplate : Type 10 E 75. Resolution 3000 l / mm.
Filter : Transmission 50 %.
LCD : Transparency LCD
Half-wave plate : 20o
Laser beam distance : Object beam = 155 cm.
Reference beam = 155 cm.
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Figure 12-13 Picture of one of the images created on the ground glass.
Image 8 :
Light power on the film : Object beam = 0.13 W.
Reference beam = 0.30 W.
Light power ratio = 0.30 W / 0.13 W
2.3:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.85 mm.
Settle time = 5 seconds.
Half-wave plate 20 o.
Exposure time = 7 seconds.
Result : The brightness of the hologram is very good, but the
vertical stripes from the slit are very pronounced.
Comments : The brightness of the hologram was satisfactory, but the problem of the embarrassing vertical lines is still not solved.
Image 9 :
The purpose of this recording is to solve the problem of vertical lines from the slit.
Light power on the film : Object beam = 0.13 W.
Reference beam = 0.30 W.
Light power ratio = 0.30 W / 0.13 W
2.3:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.71 mm.
The distance the film is to be moved between each exposure is
decreased to get a bigger overlap.
Settle time = 5 seconds.
Half-wave plate 20 o.
Exposure time = 7 seconds.
Result : The brightness of the hologram is still very good, but
the vertical lines from the slit should be less visible.
Comments : The size of the vertical lines on the hologram is
not reduced. There will be further efforts to solve
the problem.
Image 10 :
The optical set-up is the same as used earlier in this experiment.
Light power on the film : Object beam = 0.13 W.
Reference beam = 0.30 W.
Light power ratio = 0.30 W / 0.13 W
2.3:1
Slit width = 1.90 mm.
Distance the film is to be moved = 1.64 mm.
The distance the film is to be moved between each exposure is
decreased even more to get a bigger overlap.
Settle time = 5 seconds.
Half-wave plate 20 o.
Exposure time = 7 seconds.
Result : The brightness of the hologram is very good, and the
vertical lines on the hologram are minimal. The quality of
this hologram is quite satisfactory.
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Figure 11-28 Picture of a holographic transmission multi-streogram.
Comments : The real image is very bright and we have a perfect size for use as master hologram.
