Figure 12-22 The optical set-up for recording 2-step rainbow hologram (seen from above).
The focal point for the transmission master hologram (H1) is 13 cm behind the hologram. This is the distance between the master hologram and the film (H2) in the optical set-up. The filmplate (H2) is also placed in the focal point of the transmission master hologram. Light from the reference beam illuminates the film plate with a incident angle of 30 degrees.
An other important parameter is the width of the slit, it is set
to 2 mm.
Figure 12-23 Location of optical equipment.
Figure 12-24 shows a picture of the master hologram with vertical and horizontal slits.
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 40
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 3 %S.
Laser beam distance : Object beam = 175 cm.
Reference beam = 176 cm.
Image 1 :
The optical set-up for the exposure of this image is the same
as shown in figure 12-22, where the slit is placed in front of
the master transmission hologram, and is located in the vertical
direction.
Light power on the film: Object beam = 0.14 W.
Reference beam = 0.38 W.
Light power ratio = 0.38 W / 0.14 W 
2.7 :1
Exposure time = 10 seconds.
Result : The brightness of the rainbow hologram is good, but the
image has no depth.
Comments : The image has no depth because the position of the
slit is wrong. The slit must be turned 90 to the horizontal
position. This is because the master transmission hologram
is exposed with horizontal parallax.
Image 2 :
The optical set-up for this image is the same as used for the
exposure of image 1. The slit in front of the master hologram
is turned 90 in the horizontal direction. This is done to give
the image of the rainbow hologram depth.
Light power on the film: Object beam = 0.08 W.
Reference beam = 0.35 W.
Light power ratio = 0.35 W / 0.08 W 4.4 :1
Exposure time = 10 seconds.
Result : The brightness of the rainbow hologram is good and the
depth of the image is also good. The angle of the incident
light used for the reconstruction could be bigger.
Comments : The slit's position is decisive for the depth of the hologram image. If the slit had been in a vertical position and the master hologram is made with the same direction of the slit, only one or two images will be illuminated during the copying process of the rainbow hologram. With the use of a slit in the horizontal direction a part of all of the 70 images on the master hologram will be illuminated. The produced rainbow hologram then consists of 70 different images. The rainbow hologram has a image of 3 dimensions, and the depth is achieved.
Image 3 :
This image is made to make a rainbow hologram with a larger reconstruction
angle. With a larger reconstruction angle, it will be easier to
reconstruct the hologram. The light from the reference beam has
incident angle of 45. This angle is the same the incident light
has in the reconstruction of the rainbow hologram.
Figure 12-25 Location of optical equipment.
The reference beam is not parallel, but is weakly converging.
Light power on the film: Object beam = 0.08 W.
Reference beam = 0.42 W.
Light power ratio = 0.42 W / 0.08 W 5.3 :1
Exposure time = 10 seconds.
Result : The quality of the rainbow hologram is good.
Comments : It is more advantageous to use a big incident angle of the reference beam, because it is easier to use a bigger angle than a smaller angle in reconstruction. An incident angle of 45 for the reference beam is practical in this case.
Image 4 :
The optical set-up for this image is the same as used for the
exposure of image 3. In the recording of image 3, the exposure
was made with a converging reference beam. In this exposure the
recording will be made with a diverging reference beam. The purpose
of the change from converging to diverging reference beam is to
see if it makes any difference in the quality of the hologram.
Light power on the film: Object beam = 0.08 W.
Reference beam = 0.27 W.
Light power ratio = 0.27 W / 0.08 W 3.4 :1
Exposure time = 12 seconds.
Result : The rainbow hologram is good.
Comments : The brightness for image 3 is better than for this image. In this experiment, the best result were with the hologram exposed with converging reference beam.
Image 5 :
This image is made with the same set-up as used in the production of image 3 and 4. The reference beam is converging during the exposure of this image. The purpose is to make the rainbow hologram as good as possible.
The spatial filter is tuned to the object beam which illuminates
the film with maximum light energy.
Light power on the film: Object beam = 0.10 W.
Reference beam = 0.55 W.
Light power ratio = 0.55 W / 0.10 W 5.5 :1
Exposure time = 15 seconds.
Result : The quality of the rainbow hologram is very good.
Comments : The desirable quality of the rainbow hologram is achieved.
All of the rainbow images produced in this experiment had some pattern in the filmplates emulsion. This pattern is caused by light reflection on the filmplate. To solve this problem the thickness of the filmplate is changed from 1.5 mm plates to 3 mm thick film plates.
Image 6 :
The optical set-up of recording image 6 is the same as used under
the exposure of image 5. The filmplate used in this exposure is
8 E 75 HD film with the thickness of 3 mm and a resolution at
5000 lines/mm.
Light power on the film: Object beam = 0.10 W.
Reference beam = 0.55 W.
Light power ratio = 0.55 W / 0.10 W 5.5 :1
Exposure time = 150 seconds.
Result : The quality of the rainbow hologram is very good.
Comments : The problem with the undesirable pattern on the film emulsion is solved.
