Holography


written by Emily Soyka

external image brainskull.gif
Holography is the term for the study, and creation of 'holograms'. Hologram comes from the Greek words holo, meaning whole and gramma, meaning message. Essentially, holography is a type of 'lenseless photography' wherein an image is captured not as an image focused on film but as an interference pattern at the film.[1] It is an optic science dating back to 1947 when a British/ Hungarian Scientist by the name of Dennis Gabor was attempting to improve the resolution of an electron microscope, and thus came up with the theory of holography during his research .[2] Holography uses laser sights to record the patterns of light waves that are reflected from an object onto an emulsion that is made of light sensitive film or glass plates. The film is then developed and re-exposed to laser light or normal incandescent light and thus creates all the points of light that originally came from the object. The resulting imagine is either behind the film or in front of it and has all the dimensions of the original object.

Types:

Holograms can be split into two different types: reflection holograms and transmission holograms. However, between these two types, different variations can be made.


Reflection Holograms:

This is the most common type of hologram shown in galleries. It is a hologram in which a truly three dimensional image is seen near the surface. The hologram is illuminated by a spot of white incandescent light on the viewers side or front at a specific angle and distance. Thus the hologram reflects the light and creates the image. In recent years, these holograms have been made and displayed in colour, making them optically indistinguishable from their original object. Now, if the object is a mirror, the holographic image reflects white light; if the object is a diamond, the holographic image appears to 'sparkle'. Although mass-produced holograms such as the eagle on the VISA card are viewed with reflected light, they are in reality transmission holograms “mirrorized” with a layer of aluminum. Depending on the film emulsion used, images with different characteristics will be produced. The three main emulsion choices include: Silver Halide, Dichromated Gelatina and Photo Polymer.[3] Silver halide glass plates are the top choice among artists and photographers as it produces the best quality image. Holographers often use the silver halide film as it is cheaper, easier to handle and less fragile; however it doesn't produce the depth, resolution and production attainable through glass plates. The film does last longer in runs though than the glass plates. Dichromated gelatin (DCG) is a chemicle-gelatin mix coated onto glass. DCG produces very bright images in a golden-yellow colour. The images have the least range of depth but can be viewed in normal room lighting. This makes them suitable as small gift products but have been largely replaced by cheaper mass produced photo polymer holograms. Photo polymer is the newest of the recording materials. It was developed by Polariod and Dupont, has a plastic backing and is suitable for long production runs. The image depth is slightly lower then silver halide, however the images are brighter and have a wider angle of view.

Transmission Holograms:

A typical transmission hologram is viewed with laser light usually made of the same type used in the recording of the image. The light is directed from behind the hologram and the image is transmitted to the viewer's side. The type of image viewed is virtual and can be very sharp and deep. If this type of hologram is broken up into smaller pieces, one can still see the entire image, but depending on where the piece was broken off from you will see different angles. Now, if an un-diverged laser beam is directed backwards (relative to the reference beam) through the hologram, a real image can be directed onto a screen at the original position of the object. There are two methods of viewing and creating transmission holograms: laser and white light. A laser transmission hologram is made of course with a laser, but they must also be lit with a laser to be viewed. Because of this, often times the hologram appears red, as the common laser used is a helium neon laser. Other types of holograms use laser transmission as the master from which other copies are made. It is also the earliest type of hologram developed by Leith and Upatniks in 1962. White light transmission holograms are illuminated with incandescent light and produce the rainbow spectrum of colours when viewed. Because of the control holographers have gained over the colours displayed, they are able to display images in a specific colour or in their nearly full, natural colour.

Variations:

  • Embossed Holograms: A type of hologram used in cheap mass productions for security purposes. The hologram is usually recorded on a photosensitive material called photoresist. When developed, the hologram consists of grooves on the surface. A layer of nickel is deposited on this hologram and then peeled off, resulting in a metallic “shim.” The shim is then placed on a roller under high temperature and pressure where the shim embosses the hologram onto a composite material that's similar to Mylar.
  • Integral Holograms: A transmission or reflection hologram can be made of a series of photographs of an object. The object is then scanned by a camera at different angles, and each angle is then shown on an LCD screen that has been illuminated by laser light. This light is used as the object beam and is used to record a hologram on a narrow, vertical strip of holographic plate or holoplate. Each angle is similarly recorded on an adjacent strip until all angles are recorded.
  • Holographic Interferometry: The microscopic changes on an object can be measured quantitatively by making two exposures on a changing object. The two images then interfere with each other and allow fringes to be seen on the object, revealing it's vector displacement. In real-time holographic interferometry, the virtual image of the object and the real object are compared side by side.
  • Multichannel Holograms: By changing the angle of the viewing light on a hologram, different images can be observed.[4]
  • Computer-generated Holograms: As there are three basic elements included in holography, if two are predetermined, the third can be computed. By deciding the wavelength to be used for observation, the hologram can be designed by the computer.
  • Pulsed Holography: By using a quick, intense burst of laser light, it's possible to record and show movements without the movement becoming a hindering factor. This type is similar to strobe or flash photography.

How It's Made:

How a hologram is made: Diagram
How a hologram is made: Diagram
To create a hologram, a beam of light is separated into two separate beams using a beam splitter. The first, the reference beam, is directed towards the holographic film, and expanded using a diverging lens so as to cover the entirety of the film. The second, the object beam, is directed at the subject to be recorded then expanded to illuminate it. When the object beam reflects off the subject, it brings information about its size, location, shape and texture with it. The object beam then meets the reference beam at the holographic film, producing an interference pattern that is recorded in the light sensitive emulsion. Holographers use relatively the same kind of film as photographers, but it's slower, requires longer exposure time, has a finer resolution, and is more sensitive to red light. The processing involves the same developer as used in photography: hypo and fixer. Bleaches can then be used to brighten the image or more exotic chemicles can be used to shrink or swell the emulsion in order to control the colour. Once the film is developed, it is then illuminated at the same angle as the reference beam to show the 3-D image. Holograms must be illuminated to reveal an image. The illuminant can often be as simple as incandescent light.


NOTE: To see a hologram, the viewer must look at the film. 'Projected' images appear between the space of the viewer and film. There is no current technology with the ability to project an aerial or focused image into an open space without some type of smoke, mist, film or concave mirror. A hologram can produce its own real or virtual image in space, but only when its viewed through, or reflected from the physical film.


Societal Applications:

Some of the applications that holography can present to society as a whole include improvements in: security, media storage (such as the disk drives in your computer), 3-D imaging (such as the kind used in x-rays and other forms of medical imaging), and media display (television screens, monitors, etc). Since it's been noted that aerial images in an open spaces have not yet been created, instead the application lies in the ability to form clearer images through television sets and monitors with higher resolution, and greater realism. Holograms have already been used in the improvement of security but are still being perfected and have a long way to go before they reach perfection. However, since the theory was discovered in the late 1940's, holograms have already been implemented on everyday items such as credit cards and bank cards. As for holography's relation to media storage, it can be said that without holography, things such as disk drives in your computer, or x-box wouldn't be around. Holography also has great potential in the medical field of today as medical images are still seen on 2-D on screens, with the possible improvements that
can be made in holography, the technology used in the medical industry can also be improved. For example, instead of seeing an image on a screen of a 2-D brain, eventually it will be possible to
examine the brain in 3-D with greater precision and resolution. However, since holography's discovery, it has already aided doctors and researchers in understanding the human brain. In the late 1960's a man by the name of Karl Pribram ran experiments on patients brains by removing small then greater chunks. He found their memory became hazier and hazier but they never lost any specific memories. He soon found a paper in the 'Scientific American' describing the construction of a laser hologram, and hypothesized that the brain itself was operating in a holographic manner. Pribram hypothesized that the neurons, axions, and dendrites of the brain create wave-like patterns that cause an interference pattern. In 1966 he published his findings and during the next few years, refined his theory. According to Pribram, a holographic theory explains many of the mysteries of the brain, including the enormous capacity of the brain for the storage and retrieval of information.
[5] In 1981 Anatomist Paul Pietsch couldn't believe Pribram's theory, and attempted to disprove the holographic theory of the brain. After performing thousands of operations on salamanders, it was discovered that the mind perceives and stores information by encoding and decoding complex interference patterns. To summarize, through the discovery and application of holography, the understanding of the human brain has already taken giant leaps forward, and through further research, our understanding can still be increased.

Interesting Facts:

The ideas and possibilities of holography have wondered the minds of science fiction writers, artists and lovers for years. Ranging from the lovable cartoon the Jetsons, to Star Trek. The possibilities have even been included in popular video games such as Halo: Cortana for example. Even though the creation of a hologram in an open space like Cortana isn't yet possible, through the years we may be lucky enough to see the technology come to fruition. However, in the meantime, you too can create your own holograms...

How to Hand Draw a Hologram:

Obtain a small piece of acrylic plastic and a good, non-wobbly set of "dividers" (a compass with two points.) The compass must be the type with an adjusting screw to set the spacing of the points. Or, you can use a 4-in. piece of wood with a couple of finishing nails driven through it to form a pair of points. For the plastic, a CDROM 'jewel case' works fine. Next, use a marker to draw a simple pattern such as the letter "V" near the lower edge of the plate. This will be the image that we'll encode onto the surface. Draw your "V" less than 1 in. tall (2cm). Set the spacing of the compass points to a couple of inches. Place one point on the tip of the small "V" at the bottom of the plate, and *gently* drag the other point lightly across the plastic so you make an arc-shaped scratch. This is your first scratch. It helps to tilt the compass so the point trails across the surface and does not dig in or chatter. The scratch should be easily visible, but not extremely deep. The scratch should be dark and polished, not white and dusty. It should show a small highlight when viewed in sunlight or under a pointsource illuminator such as a small, clear light bulb. Now, while keeping the dividers at exactly the same spacing, place the point at a different place on the little "V" and use the other point to make a single circular scratch as before. Do this again and again, ten times or more, each time placing the point on a different spot on the little "V". When completed, the overlapping arc-shaped scratches should look like you've swept a bit of sandpaper across the top of the plastic plate. The little letter "V" should be full of holes made by the other point of the compass. To view the resulting hologram image, observe the scratches in sunlight. If your plate is transparent it helps to place something black behind it, or to paint the rear surface dark for contrast. While holding the plate chest-high with the little "V" towards your body, rotate yourself around so you face the sun, tilt
Cortana as seen in Halo 3
Cortana as seen in Halo 3

the plate up and down, and look at the scratches. At a certain angle you will see a moving highlight in the scratches. It will look like a collection of little stars, a mini- constellation in the shape of the letter "V". That's the hologram. If you go back and add more and more scratches in between the ones you already made, eventually your letter "V" hologram will look like solid white lines rather than rows of stars. When viewed with both eyes open, the "V" seems to float deep within the plastic. Its virtual depth is determined by the compass: if the spacing of the points was set to 1 in., the image appears 1 in. below the plastic surface. You can also hold the plate upside down, with the scratches at the edge of the plate towards your body, and the holographic image will float in space above the plate.[6]


Glossary:

Beam Splitter - A device used to divide the light from the laser into two separate beams - the reference and object beams. It consists of a partially transparent mirror which reflects part of the laser beam and transmits the rest.
Composite - a strong lightweight material developed in a laboratory; fibres of more than one kind are bonded together.
Emboss(ing)-is the process whereby a surface relief hologram on a nickel shim is transferred to a relatively inexpensive plastic film. The shim or shims are mounted onto a cylinder and pressed into a thermoplastic film with heat and pressure. If the film is a
tough plastic such as polyester, or is coated with a thin layer of metal to make it reflective, the process is called hard embossing and the lifetime of the embossing shim is relatively short.
Emulsion - a suspension of tiny droplets of one liquid in a second liquid. By making an emulsion, one can mix two liquids that ordinarily do not mix well.
Interference Pattern- when two waves overlap, their amplitudes add at every point. This results in an interference pattern which records the relative phase relationships between the two waves, storing each individual wave's characteristics. This is how a hologram works.Photographic emulsion is a compositon sensitive to some or all of the actinic rays of light, consisting of one or more of the silver halides suspended in gelatin, applied in a thin layer to one surface of a film or the like.
Incandescent Light - The emission of visible light from a substance or object as a result of heating it to a high temperature.
Lenses - are devices which redirect light. In photography, lenses are used to focus an image for the film. Holographers use lenses to widen the lasers beam to illuminate all of the subject which is to be holographed.
Mylar - an extraordinarily strong polyester film that was developed in the early 1950s. During the 1960s cellophane gave way steadily to Mylar with its superior strength, heat resistance, and excellent insulating properties. The unique qualities of Mylar made new consumer markets in magnetic audio and video tape, capacitor dielectrics, packaging and batteries possible.
Object Beam - the light from the laser beam that illuminates the object, and is reflected to the holographic film.
Photosensitive - meaning sensitive to electromagnetic radiation, especially light.
Reference Beam - the portion of the laser beam that goes directly to the holographic film. The interference pattern which results from the object beam meeting the reference beam at the holographic film is recorded on the film.
Shim - a 'shim' is a thin plate of metal, usually nickel, which is attached to a cylinder in preparation for the embossing process. The shim is produced by an electro-deposition process whereby the plate with the recombined images is immersed into a galvanic tank and metallic nickel is caused to accumulate on its surface. This metal plate is usually referred to as the 'master' or 'mother' shim. It is usually used to prepare 'daughter' shims which are used for the mechanical embossing process.
Vector Displacement - a vector, or the magnitude of a vector, that points from an initial position of a body or reference frame to a subsequent position.
Virtual Image - are images that are formed in locations where light does not actually reach. Light does not actually pass through the location on the other side of the mirror; it only appears to an observer as though the light is coming from this location

Further Reading:

-http://www.holo.com/holo//book/book.html
-http://hyperphysics.phy-astr.gsu.edu/hbase/optmod/holog.html
-http://www.holoworld.com/
-http://www.holography.ru/neteng.htm
-http://www.holography-news.com/
-http://spie.org/


References:


  1. ^
    Holography. (n.d.). Hyper Physics. Retrieved May 26, 2012, from hyperphysics.phy-astr.gsu.edu/hbase/optmod/holog.html
  2. ^ 1960s, t. l. (n.d.). HOLOPHILE, INC., The History and Development of Holography, hologram, holograms, holography, holography exhibitions, holographic images, 3-D, 3-dimensional images, Hologram, Holograms, Holography, Holography Exhibitions, Holographic Images, 3-D, 3-Dimensional Images. HOLOPHILE, INC. hologram, holograms, holography, holographic projection, Paul D. Barefoot, hologram projector, hologram projection, holograph projection, holographic technology, holography technology, holography exhibitions, holographic images, hologram displays, holographic projection, hologram projection, holograph projection, transparent video screen, holographic projector, hologram projector, volumetric, volumetric display, holography, 3-dimensional images, theme park, effects, laser, projector, 3D effects, stereograms, themed entertainment, laser displays, 3-D, 3D projection, holograms, three dimensional displays, three dimensional projection, 3-D projection, holographic, display, movie, parabolic, holographic tv, holographic video, parabolic projection"holographic portraits, holography portraiture, 3D projection, hologram pictures, 3-D, 3-dimensional images, lenticular imagery, lenticulars, 3D holographic projection systems, 3d holographic images, Spectral Imagery, Holography Exhibitions, Holographic Images, 3-D, 3-Dimensional Images, three dimensional projection, 3-D projection, holographic, display, 3D effects, us holographics, us holography, us holographers, tradeshow displays, holographic displays, holography technology, hologram technology, 3d projection, holographic projection, 3d holograms, corporate portraits, corporate lobby displays, corporate ecxhibitions, 3d kiosks. Retrieved May 27, 2012, from http://www.holophile.com/history.htm
  3. ^
    HOLOPHILE, INC., About Holography, hologram, holograms, holography, holograph, holography exhibitions, holographic images, 3-D, 3-dimensional images, Hologram, Holograms, Holography, Holography Exhibitions, Holographic Images, 3-D, 3-Dimensional Images. (n.d.).HOLOPHILE, INC. hologram, holograms, holography, holographic projection, Paul D. Barefoot, hologram projector, hologram projection, holograph projection, holographic technology, holography technology, holography exhibitions, holographic images, hologram displays, holographic projection, hologram projection, holograph projection, transparent video screen, holographic projector, hologram projector, volumetric, volumetric display, holography, 3-dimensional images, theme park, effects, laser, projector, 3D effects, stereograms, themed entertainment, laser displays, 3-D, 3D projection, holograms, three dimensional displays, three dimensional projection, 3-D projection, holographic, display, movie, parabolic, holographic tv, holographic video, parabolic projection"holographic portraits, holography portraiture, 3D projection, hologram pictures, 3-D, 3-dimensional images, lenticular imagery, lenticulars, 3D holographic projection systems, 3d holographic images, Spectral Imagery, Holography Exhibitions, Holographic Images, 3-D, 3-Dimensional Images, three dimensional projection, 3-D projection, holographic, display, 3D effects, us holographics, us holography, us holographers, tradeshow displays, holographic displays, holography technology, hologram technology, 3d projection, holographic projection, 3d holograms, corporate portraits, corporate lobby displays, corporate ecxhibitions, 3d kiosks. Retrieved May 27, 2012, from http://www.holophile.com/html/about.htm
  4. ^ Jeong, T. H. (n.d.). Basic Principles and Applications of Holography.Fundamentals of Photonics . Retrieved May 26, 2012, from spie.org/Documents/Publications/00%20STEP
  5. ^ Walonick, D. S. (n.d.). A Holographic View of Reality. Selected Survey Research Topics. Retrieved May 27, 2012, from http://www.statpac.org/walonick/reality.htm
  6. ^ Beaty, W. J. (n.d.). Holography without Lasers: Hand-drawn Holograms [SCIENCE HOBBYIST].SCIENCE HOBBYIST: Top Page. Retrieved May 27, 2012, from http://www.amasci.com/amateur/holo1.ht