Holography
Angel Eduardo Rodríguez Fernández
Department of Physics, University of California, San Diego, La Jolla CA 92093, USA
Physics 173
June 11, 2013
3 goals were pursued; first make a succesful transmission hologram with a holographic film, then make a double exposure on the
same film changing the angle of the reference beam, so that we can make a 2 frame “movie” and finally make a succesful reflexion
hologram with the holographic plates. We succeeded on the first and third goals. For these goals we show a useful chart that can be
used as a guide for making successful holograms. Discussion about what is left to do and why some goals didn't worked out are on
the conclusion part.
I. Introduction and Theory.
A light wavefront can be described with a simple sinusoidal wave, so if we actually know the amplitud and phase of this
sine-like wave, we know everything about it, and we can predict where it will be after certain time.
A common photograph of an object is recording the intensity of the light that the object scatters. This gives us incomplete
information about the object, and that's why we see only one perspective of the object. But as mentioned before, if we could
know both the amplitude and the phase we would be able to store all the information of the object so then we can
reconstruct the wavefront making the illusion of an object that's not there. This is the idea of a hologram.
In order to capture both the intensity and the phase of a wavefront we use interference. A interference pattern depends both
on the phase and amplitude of the waves, that's why it's the basis of holography. An actual hologram it's just an interference
pattern. You can think of a vinyl record, it has all the information so that you can reproduce the music as if the orchestra
were there. The actual details of the setup depend on the type of hologram, but basically it consists on two parts, a beam that
will go directly to the holographic film or plate (called the reference beam) and the beam that will go to the object and then
it will scatter to the film (called the object beam) interfering with the reference beam. We will work with reflection and
transmission holograms. These two will be described on the experiment section.
To get interference, we need to use coherent light. We used a laser for this purpose, but even lasers have a lot of noise, so the
beam must be “cleaned” before it can be used. We know that a perfect laser will have a gaussian shape, but real lasers have
small oscillations before the amplitude fades out (see fig. 0). Following Edmund Optics 1 site, we found out that the pinhole
size must be between 15 and 20 μm for our laser (around 2 mm diameter and a wavelenght of 632 μm).
Fig.0. Spatial Filtering setup taken from Edmund Optics1 website.
II. Experiment.
The setups for each part of the experiments change, even if they are the same kind of hologram. We will proceed to explain
the setup for each one individually, but we filtered the laser beam putting a 20 or 25 μm pinhole a focal lenght away from a
2.5 cm lens for all the setups, so we won't mention this on all of them. All the exposure and developing had to be done in a
dark room to avoid the films or plates to get exposed from unnecessary light sources.
The film we used was a Red Star holographic film, and the plate we used was the Thorlabs PHR63 holographic plate. For
a long shelf life of the plates, it's recommended to store them at 4°C. In the result data we will discuss the beam size and
exposure times. We used a 7 mW power red laser, but the value of the intensity after the filtering (after the pinhole) is the
important one, and it's the one reported on the results part. In some exposures a red light filter was used to reduce the
intensity of the laser, because without it the film overexposes in a very short time. This values are also specified on the
results section.
2.1. Transmission Hologram.
A transmission Hologram is made by exposing the film on one side with the original laser beam and the light scattered from
the object. The distance the light travels on each path (both reference and object beams) must be the same, within a few
centimeters as ilustrated on fig 1:
Fig 1. How a transmission hologram is made6.
2.1.1. Single Exposure on a Holographic Film.
For the single exposure hologram, we built a setup as in fig 1, and we show it on fig 2. Basically we have the laser going
through the space filter (with a 25 μm pinhole), and then control its size with the lens right after the pinhole. We used a 5
cm lens for small beam size and a 2.5 cm for big size. After that, the laser goes through the beam splitter. The beam splitter
we used was such that we can rotate it to change the intensity of the beams, in other words this was not a regular 50-50
beam splitter but a beam splitter with control of the intensities of both the reflected and transmited beams. We used a 2:1
Object to reference beam ratio on all the following setups. The beam going through the beam splitter is the object beam, so
this had twice the intensity of the beam reflecting (the reference beam). Then the paths follow the way of fig 1, one goes
directly to the film, and the other goes to the objet and then to the film. We used a piece of thread to measure the path of
both beams in order to make them as similar as posible. Finally for holding the film we used two flat pieces of plexiglass to
press the film and keep it flat.
When the setup is ready, you turn off the lights, take out and cut a piece of the film and put it between the plexiglass plates.
Then wait from 30 to 60 seconds to let vibrations go away and then turn on the laser for the desired amount of exposure
time. After that the film is taken to the developing process described on section 2.1.3.
2.1.2. Double Exposure on a Holographic Film.
The only difference between this and the single exposure is that we change the angle of the reference beam. In order to do
that, we made the setup shown in fig. 3. As it is shown on the figure, it's the same setup as part one, only that the image was
taken from the other side and with two more mirrors. The mirror on the center, right next to the beam splitter could go down
or up, so when it was down, the reference beam followed the path on fig. 2 (and it's shown on fig 4), but when the mirror
was up, it was placed between the beam splitter and the mirror, so it reflected the beam to another mirror and then to the
film as shown on fig. 5.
Fig 2. Setup for making a single transmission hologram.
Fig 3. Setup for making a double transmission hologram.
Fig 4. Path followed by light when the middle mirror is down.
Fig 5. Path followed by light when the middle mirror is up.
So with the values we knew that worked from part 2.1.1 we exposed the film following the same instructions as before. For
example if the exposure time from part 2.1.1 was 10 seconds for a certain intensity, then we exposed the film with the
mirror down for 5 seconds and with the mirror up for another 5 seconds.
2.1.3. Developing the film and viewing the hologram.
This is a very simple process but it takes some time and should be done in a dark room. The materials used were Kodak
developer, 2% solution of acetic acid and Kodak fixer.
When te film is exposed and ready to be developed, you have to do the following steps:
–
–
–
–
Put the film on the Kodak developer for 7 minutes and agitate it every minute.
Put it for 30 seconds on the 2% acetic acid. Agitate the whole time.
Put the film on the Kodak Fix between 2 or 3 minutes. No agitation is necessary.
Wash the film with water and let it dry. This can be done with a hair blower or just letting it hang on a thread.
To view a transmission hologram after it's dry, the film is placed on the same orientation between the plexiglass plates and
the reference beam is directed to it (basically the same process as exposing the film). The film will act like a diffraction
grating and the hologram will be on the first order diffraction. One easy way to find it is to (carefully) put your eye at the
imaginary line that conects the object with the film.
2.2. Reflection Hologram.
A reflection hologram is made by exposing a holographic plate on one side with the reference beam and on the opposite side
with the light scattered from the object. There is even more freedom in this method because you can split the beam or use
only one beam.
We actually made 3 different setups for the reflection hologram. One was basically switching the film and the object from
fig. 2, making sure that the distances remain the same for both beams. We didn't succeeded with this method so we changed
the setup.
The second setup was a variation of the one suggested on Thorlabs website 2. The Thorlabs website uses only one beam, no
beam splitter, and it's easier. It is done by putting the object right next to the film, on the opposite side where the reference
beam hits the plate. This works because light goes through the plate and reflects on the object, so one beam works both as
the reference beam (when it first hits the plate) and the object beam (after it reflects from the object). Since the object is
next to the film, the path of both beams will be basically the same. The variation comes that Thorlabs suggest to put the
objects on the table horizontally, then put the film on top of the object and shine the laser to it, but for the second setup we
put everithing vertically. This setup had some vibration problems, and only worked once.
We had a small amount of plates, so we cut them into four pieces, to test the intensities and exposure times without running
out of plates. This setup is good for the whole plate, not for the quarter part of the film because it's so small (around the size
of a dollar coin) and we used big tweezers to hold it, that we were blocking part of the light.
The third and final setup we did was actually the one suggested from Thorlabs 2 (Fig. 6). We worked on this setup the most,
but that doesn't mean that this is the best one.
Fig 6. Our setup for the Thorlabs suggested method.
The exposure method is the same as the film. It needs to be on a dark room, you put the film on top of the object, wait
around 30-60 seconds to avoid vibrations and expose the plate by turning on the laser, however, the developing procedure is
different.
2.2.1 Developing and viewing the holographic plate.
We ordered the PHRKIT from thorlabs because different chemicals were requiered. The developing instructions can be
found on the manual of the PHRKIT2.
We need to make 3 solutions, part A, part B and bleach. We will list the chemicals for each part:
Part A:
-4 g of Metol or Elon
-25 g of Ascorbic acid (powder)
-1000 ml of distilled or deionized Water.
Part B:
-60 g of Sodium Carbonate, Anhyd.
-15 g of Sodium Hydroxide (Hazardous chemical)
-1000 ml of distilled or deionized Water.
Bleach:
-35 g of Copper Sulfate Pentahydrate.
-100 g of Potassium Bromide.
-5 g of Sodium Bisulfate, Monohydrate.
-1000 ml of distilled or deionized Water.
The instructions are the same for each part: Dissolve each chemical one by one on the water. Warming the water makes this
process easier. Part A must be refrigerated or inside a container with little airspace.
The developing process is simple. Mix the same amount of part A and B on a container. Have ready two more containers
filled with distilled or deionized water and one more with the bleach. The plate must be totally covered by these solutions.
After you exposed the film, you follow these instructions (on a dark room) to develop it:
–
–
–
–
–
–
Put it for 20 seconds on the Part A & B solution and agitate. The plate should turn really dark.
Rinse it between 30 seconds and 3 minutes on one of the deionized water containers.
Put it on the Bleach around 2 minutes. The plate should turn transparent again. You can turn on the lights after this
part.
Rinse it between 30 seconds and 3 minutes on the other deionized water container.
Let it dry on clean air (can take hours) or use a hair blower.
Optional. Use Photoflo for clearer images.
To see the hologram, you need to direct a white bright light to the plate and find the angle (the exposure one) where you can
see the object. The sun, a bright led, a bright lightbulb and even the reference beam work. Contrary to the transmission
hologram, you have to see the plate on the same side where you direct the light.
III.Results and conclusions.
We show a chart with the results of each experiment at the annex.
We obtained succesfull holograms on the first and third part of the experiment. For the first one, we saw that if the hologram
is really dark, it is easier to look even with lights on. Vibrations are really important, we couldn't get excelent resolution,
probably because of vibrations, but this part made the clearest and brightest holograms.
For the second one, one exposure never worked, making us think that the reference beam angle was such that almost all the
light was reflected by the plexiglass before getting to the film.
For the third part of the experiment, the first setup didn't worked because our object was really far away from the film
(around 30 cm). We are thinking this is the reason because even the coins that are close to the film give faint images. For
more 3-D objects, a beam splitter is needed to have a much brighter object beam. The second setup worked really good
when we hold the small plate with the tweezers, but when we just leaned the plate without holding it it didn't work. The
third setup worked really well with coins and flat objects. We suggest to try the Photoflo and see how much the image
quality improves.
We only changed the intensity and the exposure time, but there are a lot of variables in holography. A very important
variable to control is the distance between the object and the film or plate, specially for the reflection hologram and the
holographic plate, but others can be the size of the pinhole, the object/reference beam ratio, the angle of the reference beam
and vibrations. Vibrations are really important for hologram quality. Try to avoid vibrations as much as you can.
Future work can be perfecting the double hologram on a film, then doing that on the holographic plate. The plate will be
much more appealing because you can see either one or the other hologram just by rotating the film (just as the holographic
stickers on the credit cards for example, but with a real 3D image). Another great project could be measuring how many
holograms can be stored in one film or plate before it saturates.
IV. References.
1.
2.
3.
4.
Understanding Spatial Filters. Edmund Optics. http://www.edmundoptics.com/technical-resourcescenter/lasers/understanding-spatial-filters/
Holography Plates and Supplies. www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=6716
M. Parker Givens, Introduction to holography, Institute of Optics, University of Rochester, Rochester, New
York 14627.
Adams, Brian, Tim Chinowsky, & Chi-yen Wang. Holographic Interferometry of Mono- and Bimetallic
5.
6.
V.
Pennies. Feb 1995 .
Stefanie Garcia and Walter Commons. Holography and Measurement.
http://physics.ucsd.edu/neurophysics/courses/physics_173_273/Holography_2012.pdf
http://en.wikipedia.org/wiki/Holography
Acknowledgment.
Dr. Philbert S. Tsai, Professor.
Grant Allen, Teaching Assistant and part of the Holographic Team.
Film
VI. Annex
Single Exposure, film
7 mW Laser, λ = 632 nm, 25 μm pinhole
#
Object
Beam Ratio Filter Intensity [mW]
1
2:1
No
3.8
 Pile of Coins
2  Pile of Coins
2:1
No
3.8
3
 Key
2:1
No
3.8
4
5
6
 Key
 Key
 NFL Figurine
2:1
2:1
2:1
0.8
0.5
0.2
0.54
0.96
1.92
Double Exposure, film.
7 mW Laser, λ = 632 nm, 20 μm pinhole
#
Object
Beam Ratio Filter Intensity [mW]
7 a.  NFL Figurine Front
2:1
0.2
1.92
7 b.  NFL Figurine Back
“
“
“
8 a.  Peso (Front)
2:1
0.2
1.92
8 b.  Peso (Back)
“
“
“
9 a.  Peso (Front)
2:1
0.2
1.92
9 b.  Peso (Back)
“
“
“
10 a.  Peso (Front)
2:1
0.2
1.92
10 b.  Peso (Back)
“
“
“
11 a.  Peso (Front)
2:1
0.2
1.92
11 b.  Peso (Back)
“
“
“
Exp. Time [s] Beam radius [cm] Comments
10
2.5
Over exposure. Really dark interference.
2
1.5
Dark Interference, Small section of the
pile, can see hologram with lights on.
1
1.5
Medium dark interference, good and
almost clear hologram of the head.
20
4.5
No interference.
5
4.5
Faint Interference, Low exposure time.
10
4.5
Medium faint interference. Low exp. Time.
Exp. Time [s] Beam radius [cm]
10
6
“
“
15
6
“
“
20
7
“
“
20
7
“
“
25
7
“
“
Página 1
Comments
Faint hologram. Needs more exp. Time.
Faint hologram. Needs more exp. Time.
Faint hologram. Needs more exp. Time.
Faint hologram. Needs more exp. Time.
Works good. Medium dark interference.
Didn't work.
Didn't work.
Didn't work.
Worked.
Didn't work.
Plate
Single Exposure, plate. 2:1 beam ratio.
7 mW Laser, λ = 632 nm, 20 μm pinhole.
Hologram # Plate size
Object
Intensity [mW]
0
1/4 (1 inch)  Peso
4.04
I
1/4
4.04
 Peso
II
1/4
4.04
 Peso
III
1/4
4.04
 Peso
IIII
1/4
4.04
 Quarter
IIIII
1/4
4.04
 Quarter
VI
1/4
3,5
 Quarter
VII
1/4
3.5
 Quarter
VIII
1/4
3.8
 Half Quarter
IX
1/4
3.50
 Quarter
X
1/4
3.50
 Quarter
XI
1/4
3.50
 Quarter
XII
1/4
3.50
 Quarter
XIII
1/4
3.50
 Quarter
XIV
Full
3.41
 Keychain 6”
Beam radius [cm]
2.5
4
2.5
2.5
5
5
6
6
6
6
6
6
6
6
6
Página 2
Exp. Time [s]
10
60
30
15
15
7
20
15
25
22.5
30
15
10
20
20
Comments
Really Clear image (better if a led is used)
Most likeley over exposure.
Probably bad setup
Good hologram but only for a small part of the coin.
Full coin but hard to see.
Probably small exposure time
Almost perfect image.
Almost perfect image.
Bad placement of quarter.
Almost perfect image.
Really Clear image of a ring part of the coin.
Hard to find the angle, but a good hologram.
Faint image of the quarter.
Blurry image.
Good hologram, needs bigger beam.