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Holograms are 3D images of real objects. In contrast to a normal photograph, in a hologram one is able to see different 'sides' of an image by looking from different angles. Hologram technology is advancing quickly and quickly becoming commercial - think TVs, museum displays etc. Plenty of cleaning services have cleaned around many of those holographic displays in New York City and Chicago museums. For cleaning information you can click http://www.cleaningservicenewyorkcity.com/services.html
Despite the apparent complexity of holography, it is entirely possible to create holograms DIY-style!
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A hologram as typically depicted in Hollywood
(Image adapted from original by Sean Martell) |
Image of the laser used to construct Penguin's Lab holograms.
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So, how do holograms work anyway?
Think back to a normal photograph. What you see is a reproduction of the light which entered the camera shutter at the time. In other words, the photograph depicts the relative amplitudes of light entering the shutter.
On the other hand, what you don't see in a normal photo is depth. If the human eye had no sense of perspective in the real world, then one would be unable to distinguish foreground from background. Think of a typical Picasso work - perspective is questioned and the result seems artistic rather than realistic.
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In essence, what a normal photograph fails to capture is the phase of light entering the shutter. The phase essentially contains information on how far the light wave has travelled - a crucial measure of depth.
Holography enables the capture of light phase by 'comparing' the incoming light with a reference beam shone at a different angle. Both beams are shot onto a photographic plate - the resulting pattern is what we call a hologram.
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'Comparing' different phases of light to produce a hologram
(Image courtesy of Wikipedia org)
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Recreating the image
(Image courtesy of Wikipedia org)
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To recreate the virtual image, a beam of light known as the reconstruction beam is shone back onto the photographic plate at an appropriate angle.
Since both amplitude and phase are recorded onto the photographic plate, the viewer is able to see a three dimensional reproduction of the original object. In fact, the viewer can see 'hidden' sides of the object by turning his/her head.
For a hologram to work properly, however, the phase of the light must be consistent. In other words, the light source must be monochromatic. The most obvious way to achieve this is to use a laser. For the creation of my holograms, the green DPSS laser was used.
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Usually holography is carried out on an optical table with special vibration reduction systems, since vibrations of as little as a few micrometers can completely wreck a hologram. We are talking vibrations like air currents, footsteps, loud music and even changes in temperature!
The room I used had a concrete floor and was at ground level. Vibrations were also tested for using a Michelson Interferometer setup (bottom right). This involves splitting the laser beam using a prism onto mirrors, then recombining these beams and spreading the beam with a diverging lens, so that minute interference patterns are visible (top right).
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Testing for vibration using a Michelson Inteferometer |
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Preparing the chemical solutions....
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I used the following solutions for development of the holographic film:
Developer:
- 20g Catechol
- 10g Ascorbic Acid
- 10g Sodium Sulfite
- 75g Urea
- 60g Sodium Carbonate, Anhyd.
- 2000mL Distilled water
Bleach:
- 5g Potassium Dichromate
- 80g Sodium Bisulfate
- 1000mL Distilled water
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Holographic film was supplied by Integraf. I used VRP-M film, which is sensitive to green light.
I needed a holder to securely clamp the film during exposure. This was made using two sheets of glass, some super glue, some paper clamps, and 5 minutes of work.
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Inspecting a newly made hologram
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A typical exposure of mine involves the following process:
- Prepare everything... chemicals, film, optical setups, turn on laser (with shutter DOWN, so no output)
- ALL lights are switched OFF, red safelights are switched ON.
- Film is cut up into appropriately sized bits
- Film is loaded into film holder and set up in position
- Fans are turned OFF, silence for at least 2 minutes
- Laser shutter is momentarily lifted, for about 1 second
- Fans are turned ON, and film is retrieved from holder
- Film is put in developer solution, rinsed, put in bleach solution, rinsed, then left to dry.
- Lights are turned ON
- Inspection of hologram.
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So, lets see some results... bear in mind with these pictures that obviously these are normal photos of holograms of objects - therefore they do not possess the same dynamic 3D characteristics as the holograms themselves!
To the right is a (single beam transmission) hologram of a glass angel figurine.
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Here is an Australian 50 cent coin. This is one of my favourite, but it is dimmer than some others.
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This is a (single beam transmission) hologram of a glass kangaroo key ring. I like this one, as it has a lot of depth. The words are also quite clear.
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Here is a hologram from a different point of view which really highlights the way some of these images can 'stick out' from the film and appear to be hovering in mid-air.
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Here is a (bad quality) reflection hologram of a bunch of coins made quite recently.
Reflection holograms are exposed in a slightly different way to transmission holograms (such as those above). They are, however, slightly more prone to vibrations, and do not offer much depth of field.
An advantage of reflection holograms is that you don't need to bring a laser along to view them, all that's needed is a bright source of white light (eg. halogen lamp, or normal incandescent).
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