Holography

From WolfWikis

Introduction And History

What is Holography?

Hologram from MIT Muesum^[1]

Holography - is the process of capturing three-dimensional images by recording patterns of light wave reflection. These recorded holograms are viewed by re-exposing the developed film to light in order to recreate the pattern of light recorded. When viewing a hologram, the original object appears to be floating in space, and it retains its properties of perspective. That is to say, the observer is able to see the object from different angles as his frame of reference changes, just as would be seen with a "real" object. This attribute can likely be associated with holograms essentially consisting of light.

Holograms come in two basic types:

• Reflection holograms - reflect light to the viewer from the front.
• Transmission holograms - bend the light from the back of the hologram as it passes towards the eyes of the viewer.^[2]

Why is Holography Important?

You do not need to go far to see a hologram. Your driver's license and credit cards most likely contain a hologram to prevent counterfeiting. You probably own a number of products making use of holograms.

Today holography is available everywhere. Mass produced holograms are commonly featured on currency, credit cards and documents as a security measure against counterfeiting. The visual appeal of holography has gained the interest of both artists and advertising. Books and magazines often have holographic covers. Product packaging and products themselves often use holograms as ways of captivating the consumer's interest, while helping protect against counterfeiting. Holograms can be of great help in analysis of an object for miscellaneous purposes. A variety of medical technologies, such as MRIs (Magnetic Resonance Imaging) and ultrasounds, make use of holographic techniques. Holograms are commonly featured in the movies and other media. ^[3]

The use of holograms as a storage media could significantly improve the performance of computers in the future. ^[4]

Dennis Gabor, discovered holography ^[5]

Discovery

Holography was first developed by Dennis Gabor, a British scientist native to Hungary, in 1947. Gabor stumbled upon holography while researching ways to improve the resolution of his electron microscope. He termed his discovery as hologram from the Greek words holos, which means "whole", and gramma, which means "message". This together makes "whole message," which refers to the ability to capture all perspectives of an image. ^[5] Gabor later received the Nobel Prize for his work in 1971.

Gabor's hologram used a mercury lamp as a light source. A lack of uniform, consistent light waves caused his holograms to contain many shortcomings, such as double images and aberrations. Without a perfect light source, there was little progress in holography for the next decade. However, during this period, other scientists were able to gain a better understanding of holography and build on Gabor's initial theory. ^[4]

Further Developments

Credit cards use holograms as a form of security.^[3]

In 1960 the laser was invented by A. Prokhorov, N. Bassov, and Charles Towns. Unlike white light, a laser's light waves are uniform, of equal wavelength, and consistent. These properties are what makes lasers the ideal light source for use in holography. Dr. T.H. Maimam developed the pulsed-ruby laser in 1960 as well, which is a system capable of a powerful burst of light that only last a few nanoseconds. This new developement opened up the possibility of capturing high speed events with holograms. ^[5]

Two years later in 1962 Emmet Leith and Juris Upatnieks tried applying an "off-axis" technique, from their work on side-reading radar, to Gabor's technique with the use of a laser. This allowed for the production of 3D holograms that were both clear and had a realistic sense of depth. These laser transmission holograms required the light of a laser to be viewed. With this technique, it is very important that the subject of the hologram is very stable, since movement can mess up the hologram. Leith and Juris's work led to a standardization in holography and the technique is still widely used today. Another important development in this year was a method by Dr. Yuri N. Denisyuk to produce white-reflection holograms, which are able to be seen by the light of an incandescent light bulb.

1965 saw the introduction of holographic inteferometry by Robert Powell and Karl Stetson. Holographic interferometry takes a stressed and unstressed holographic exposure of an object, and displays the distortions between the two as contours. This had useful applications for fluid flow analysis, quality control, testing materials, and such.^[4]

In 1967, the use of dichromated gelatin, a chemical-gelatin mix that produces bright golden-yellow images but records a low range of depth^[2], as a holographic recording medium was devised by Shankoff and Pennington. A hologram could then be recorded on any non-porous and clear surface. Rich Rallison later made efficient use of such dichromate holograms in the late 70s to early 80s, producing various premium items such as key chains or pendents. Other significant events of 1967 include the first mass distributed hologram, a 4" x 3" transmission view of pieces of a chess board in the World Book Encyclopedia Science Yearbook, and the opening of Editions Inc., a hologram gallery in Ann Arbor which opened the public to holography, and also the pulse laser was used to create the first hologram of a human being.

Dr. Stephen A. Benton made a significant advance in holography in 1968 with white-light transmission holography, which he discovered at Polaroid Research Laboratories while in the midst of research into holographic television. White-light transmission holograms are able to be seen in typical white light and produce a "rainbow" image from the seven colors that make up white light. The great imagery created by these "rainbow" images captivated many of the artists of the time, and increased the common public's awareness and understanding of holography as a legitimate science. Also, in the same year, the first holographic art exhibition took place at the Cranbrook Academy of Art in Michigan.

In 1970, Lloyd Cross and Gerry Pethick devised an inexpensive sand-table system for producing holograms. This made holography significantly more accessible to the public, and was of great help to artists interested in holography. Lloyd Cross also started the San Franciso School of Holography the following year, which was the first place for people to learn these new holography techniques. Then in 1972, Cross came up with the integral hologram, which used sequential 2D motion picture frames of a rotating subject in order to produce a 3D holographic stereogram.

Enabled by Benton's discovery of white-light transmission holograms, Michael Foster was able to develop an embossing technique in 1974 which allowed mass production of holograms, and this technique was made commercially viable by Steve McGreww in 1979. The process works by transferring holographic information from light sensitive glass plates to nickel embossing shims, and the interference pattern is then stamped onto plastic with a mirror backing. The hologram produced is easily replicated, and also inexpensively. Such embossed holograms have become quite common today in a variety of fields such as banking and advertisement.

In 1976, Benton was able to modify the white-light transmission holography he developed to produce achromatic holographic images (black and white). Also in 1976, the Museum of Holography opened in New York City, and Victor Komar came up with a process for projected holographic movies at the All-Union Cinema and Photographic Research Institute (NIFKI) in the U.S.S.R. A pulsed holographic camera was used to record 20 frames per second, and the film was projected onto a holographic screen which focused the image to the audience. The 47 second film could be displayed to 2 or 3 audience members. Plans were made to increase the scale, but nothing ever came of it.

In the 80s, holography furthered it's place in society for the general public. In 1983, Mastercard was the first to utilize holograms on bank cards as a form of security. And in 1984, the March issue of National Geographic was the first major publication to place a hologram on the cover. The December 1988 issue of National Geographic's cover was even entirely holographic. ^[4]

Further progress has been made in holography since, and continues to this day, where it remains an important if sometimes overlooked part of our lifestyle.

Analysis

  Lasers

Diagram of a laser ^[6]

The fundamental breakthrough for holography was the invention of the laser in 1960. As such, it is important to understand how a laser works before understanding holography.

Laser stands for Light Amplification by Stimulated Emission of Radiation. ^[7] Lasers differ from white light in that they are monochromatic and coherent. Coherent means that all emitted photons are of the same wavelength, phase and direction. This is the fundamental property that makes their use ideal for holography. ^[6]

Lasers are created by a process called stimulated emission, where a photon is used to provoke an unstable system into decaying. A cylindrical chamber is filled with about a 9/1 helium/neon gas mixture. Atoms inside a chamber are raised from ground energy E1 to a very excited state E3 or E4 using an external source of energy. Population inversion is reached when more atoms are excited than grounded. These excited atoms begin to decay into a metastable state and photons are emitted.^[6] A small percentage, 2%, will be traveling in the horizontal direction, completely parallel with the tube. ^[8].

  At either end of the chamber are silvered mirrors, which cause photons to be reflected. The photons traveling horizontally are reflected back and forth. While traveling through the chamber, photons collide into an energized atoms. This collision causes the atom

  to decay a photon in the same direction, energy and phase as the colliding photon. More and more photons begin to build up in the horizontal direction.^[8].

  One of the chamber's mirrors is only partially silvered, so that most photons are reflected, but some pass through. The photons that pass through are then released and are coherent. The result is beam of light where all photons are coherent. ^[6].

Basic set up of a hologram recording^[9]

How Holograms are made

Like photography, holography is a two-step process. First is the recording of the hologram, much like the actual shutter clicking of a camera. The second process is projection, which is analogous to developing the photograph.

Example of the exposed holographic film ^[10]

Recording Transmission Holograms

First a laser is installed and aimed at a beam splitter. The beam splitter causes the laser light is split into 2 separate beams going in different directions. One of these beams is the reference beam and the other is an object beam. Each of these is aimed with mirrors that reflect but do not alter the beam.

First, the reference beam is reflected onto the film directly. The reference beam is important and its precise location relative to the film must be noted for later. The object beam is reflected onto the object. The light bounces off the object in many directions and exposed to the film. The object beam will be the apparent light source in the resulting hologram.^[11]

Since both beams are exposed to the film, the constructive and destructive interference between the beams is recorded. The resulting exposed film is an image of concentric circles as a result of the wave interference. ^[10]

Projecting Transmission Holograms

Hologram projection^[12]

In order to project a transmission hologram, a laser is fired at the hologram. This laser must be in the same position relative to the hologram as the reference beam. The coherent light from the laser hits he hologram, which causes it to interfere, bend and change as it passes through the film.

The viewer stands on the other side of the hologram, looking through it. The light emerging from the hologram is the same as the object beam reflected off the original object. Although the real object is not really there, light is emitted from the hologram as though the hologram were a window and the object beam was the only light source. ^[12]

The remaining work is done by the eyes and the brain. Because the light patterns are emitted, each eye receives a slightly different pattern of light. The difference of light patterns is interpreted by the brain to be the difference of light patterns of light reflecting off an object and appears as a real, 3D object to the observer.^[11]

Properties of Holograms

The projected image has many interesting properties. First is that the image appears at the same distance as the hologram was from the original object. This means recording the object at a further distance results in an image at a further distance. ^[12]

Another property is that magnifying glasses held up to the original object will appear to exist perfectly in the hologram. That is, the holographic magnifying glass will really "work" and moving around. This makes sense, since a magnifying glass merely bends light and the hologram will accurately record this bent light.^[9]

Another amazing property of holograms is that a tiny section of the film contains enough information to recreate the whole object. If a hologram is split in two, both halves could completely replicate the object. ^[13]. When divided, what is lost is perspective information. This is analogous to having a very large window and then covering half of it; the uncovered half can still view the object, but the range of perspectives has been limited.^[11]

Limitations of Holograms

Animated holograms are very difficult and expensive. Understanding why requires some basic knowledge about photographic film. In order to create a sharp hologram, the film used must be extremely granular and fine. Finer film will record the interference pattern with greater detail, thus giving a higher image quality.

This very fine film requires more time to expose. In a normal photograph, any object movement during this lengthy exposure time could result in motion blurs. In holography, very small movements result in the complete destruction of the hologram. Movements as small as 1/10th of a wavelength interrupt the interference patterns records on the film, resulting in a completely trashed exposure. Normally this overcome by building stabilizing platforms and reducing vibrations in the studio. ^[14]

The trade off between time and quality means animation cannot be done well with the normal equipment. However, animation can be done with a Pulse ruby laser, which can send a laser pulse for only a few nanoseconds. This short pulse will expose the film without movement being a concern. These lasers are extremely expensive though and well beyond the reach of most holographers.^[14].

Other Types of Holograms

Holograms are differentiated by the light source used in projection. Some important types of holograms include (but are not limited to):

• Transmission holograms, as explained above, use lasers and the light source is shined through the hologram towards the observer.
• Reflection holograms use a light source (typically white light) from the same side as the viewer.
• Embossed holograms are the ones you typically see on credit cards. The inference pattern is recorded onto a metal stamp and then imprinted on cheap foil.
• Computer holograms. Using mathematical models, the inference pattern on the hologram is calculated by a computer.^[15]
• Rainbow holograms: The same image appears in different colors when viewed at different angles^[16]

Conclusion

In Summary

Before diving into the realms of the future applications for holography in today’s society, let’s take a brief look at some of the key information expressed above in order to achieve a better understanding of the topic.

Holography, briefly stated, is: 3D images captured on film by recording patterns of light reflection, made visible by the re-exposure of this film to light. While this may sound like something straight out of a sci-fi movie, holography is often used commonly in today’s society for “normal” life activities, including the use in: licenses, credit cards, advertisements (to catch the consumer’s eye), MRI machines, ultrasounds, and many others.

Some key developments in the history of holography can be attributed to the following dates/events:

• 1947 - Invention of holography
• 1960 - Invention of the laser (beneficial to holography due to the consistency of its light)
• 1974 - Mass production of holograms made possible
• 1983 - First used for security purposes on bank cards

Future Applications of Holographic Technologies

Holographic Data Storage

One of the most practical, likely, and current applications being developed in holography has to do with data storage. While Holographic Versatile discs (HVDs) have not yet been mass marketed into the economy, there have been advancements made towards the technology and its possible use in the technological market. ^[17]

So, the obvious questions that come up when introducing a new form of technology intended to replace another one (in this case HVDs replacing data CDs, DVDs, etc.) deals with its advantages and disadvantages, both of which will be addressed below.

An illustration of a Holographic versatile disc and its structure^[18]

Advantages

• Much more memory space available per disc - HVDs have been made with 300 gigabytes (GB) of space available, more than 450 CDs!. Predictions of HVDs with more than a terabyte of available memory space have been made for the future. The reason for the dramatic increase in data storage space on HVDs over a DVD or likewise, has to do with the way that the data is stored. On devices such as DVDs, data is only stored on the surface of the media, whereas for an HVD, data is stored throughout the entire thickness of the media, allowing for much more data to be stored on a disc.^[19]
• Much faster transfer rate – currently at 150 times the transfer rate of modern DVDs. This is due to the “page format” that is used in HVDs, where entire pages of information are stored at once, rather than small chunks of information.^[19]
• Longer shelf life - HVDs are predicted to have longer shelf lives than its competitors, estimated to be somewhere near 100 years or more.^[19]
• Less physical space occupied - entire libraries of information could potentially be stored on a couple of discs or drives, making information more accessible to users, and limiting the needed space, organization, time, etc. currently needed in places like libraries for example.^[19]

An illustration how holographic data storage works^[20]

Disadvantages

• COST – As always with new technology, the number one disadvantage for most new technologies are related to expenses. It’s predicted that the first holographic drives could be as much as $15,000 and the first HVDs around $120-$180.^[21] While this seems really expensive (and it is a lot of money), it’s not unusual for modern technology to start at such high prices, and considering the amount of CDs, DVDs, traditional disc drives, etc. that would be needed to do the same job, its not as costly as it may seem to be. Also, partly as a result of this price, the first productions of the aforementioned technology will likely be at first limited to enterprises, rather personal consumers.^[21] The good news is that once the business world starts to use HVDs, the price should eventually come down to a more agreeable level. Potentially at some point down the road, it is likely that the cost per GB of space will actually decrease with this mass production of this technology.
• Coinciding with the fact that it’s a new technology, and that it is and will be expensive, another big problem is that there is not really a market set up for it yet. Many consumers are not even aware of holographic data storage and its applications. Also, as a result of this, there is not really an industry set up for mass production at this point. Once the industry progresses and begins to mass produce, the technology will become more practical (and cheaper too).^[17]
• Also, another possible disadvantage that comes with the territory of technological advancements is a direct symptom of its novelty. All the estimates for the future are made based on predictions, so real world scenarios could prove to have drastically different requirements and therefore lead to different properties, attributes, etc. Also, there are no standards set up yet, and there have not really been sufficient tests run as to the limits of its uses, how it should or should not be used in the practical world, its reaction external environmental factors, etc. Early consumers may run the danger of disappointment with the applications of the technology and/or may end up with undesired complications as a result of factors not considered or predicted. Having said that, this always is the danger with any new technology developed.^[17][21][19]

Practical Application: Holographic data storage exists to some degree currently, and will almost definitely at least compete in the future technological community, if not replace all together its competitors in the end. While its use will initially be limited to enterprises due to the initially high cost, eventually the price will be reduced and become more available to the individual consumer. More than likely, holographic data storage will be the most immediate and beneficial advancement of holography as it stands today.^[19]

Holographic Media

The obvious implication of the Holographic Data Storage technology, is then the use of this technology in the media (TV, movies, etc.) This is often the aspect of holography that is represented in sci-fi movies such as Star Wars for example, and is what most people as a result think of when they hear the word "hologram".

There has recently been increasing research done for laser-based holographic players, recorders and media. For example: in 2005, in Tokyo, InPhase Technologies was the first company to use a holographic recorder to air a commercial. The fact that this short commercial being aired was such a big deal in the holographic technology world is itself an indication of the major problem associated with this use of holography.^[17]

While it is now possible to make holographic media (recordings played back), it is extremely complicated and requires a lot of time/work/equipment, and most of all is extremely expensive. A more efficient way of producing holographic media is needed in order for it to be a viable form of media, and to be used in the media industry on any sort of wide scale. More than likely, unless dramatic advancements in the field are made, due to its complexity and expense, holographic media is, at the very least, still a long way off from being accepted as competitive in the technological market, compared to the prospect of using the previously discussed holographic data storage devices. ^[17]

Also, especially with the way the economy is right now, the consumer demand for holographic players, recorders, and media is barely existent.

Practical Application: In conclusion, while Holographic media poses interesting ideas, and is not out of the realms of possibilities for future use, until advancements in the field are made to improve creation of such products, its use will remain extremely limited.^[17]

Public Perception of Holography

This analysis of holographic media leads directly into one of the biggest problem with the public's knowledge and perception of holography.

Hologram in Star Wars^[23]

Movies such as the aforementioned Star Wars, have been showing characters of the story using holographic means of communication, video and things of such nature since holography has been invented. As stated before, Holography was invented in 1947 and even mass marketed in the 70's and 80's and is not itself nearly as novel, futuristic, and new of an idea as these movies often continue to portray it to be. Often in these types of movies, the civilizations that are using holographic technology are represented to be much more advanced than our current one, and so with that, the common misconception that goes with the term holography is that it is science fiction.

Most people think of Holography Media when they hear the word holography, and don't consider the more simple, practical applications of the holographic technology that exist. Holography is every bit as part of our life today as steel and wood are. This is evident through most of its more "simplistic" uses in items such as credit cards and MRI machines. Holography presents an interesting and possibly bountiful frontier for the expansion of modern knowledge and technology.

Scientific Perception of Holography in Today's Society

The way holography is viewed scientifically is quite different from how the general public perceives it. Holography is a legitimate technological advance, with many potential applications. These applications are less obvious and not as fantastical of those common to fiction. Right now, it works as a good measure against counterfeiting, and also has an artistic appeal. The most practical future applications (at the moment) are in the direction of holographic data storage devices, and also there is a somewhat distant potential to one day also enter the realm of usefulness in the media, as a form of 3D entertainment. Holography could also be used to help scientists visualize a project/design, and is of great use in medical technologies such as MRIs. While capable of all these things, holography is not yet at the complex levels commonly seen in science fiction, such as moving holograms of people, as the technology required to do animated holograms of any meaningful sort of length is quite expensive and unpractical for current purposes. Efficiency is a big concern in the use of holography. Just like other technologies, in order to be mass marketed and widely used in society (like in the movies), Holography must achieve a level of efficiency that allows for practical means of development, and have applications that are efficient and easy enough to appeal to the general user on a consistent basis.

Works Cited

1. ↑ A, Jamie. Go Boston Card Blog: Geek Chic in Cambridge. 05 Nov. 2007. 25 Apr. 2009 <http://www.gobostoncard.com/blog/2007/11/05/geek-chic-in-cambridge/>.
2. ↑ ^2.0 2.1 Barefoot, Paul D. Holophile, Inc: About Holography. 27 Oct. 2007. 25 Apr. 2009 <http://www.holophile.com/html/about.htm>.
3. ↑ ^3.0 3.1 Hologram Suppliers. Hologram Applications. 14 Feb. 2008. 25 Apr. 2009 <http://www.hologramsuppliers.com/holograms-applications.html>.
4. ↑ ^{4.0 4.1 4.2 4.3} Barefoot, Paul D. Holophile, Inc: Holography History. 27 Oct. 2007. 25 Apr. 2009 <http://www.holophile.com/html/history.htm>.
5. ↑ ^{5.0 5.1 5.2} Holography Virtual Gallery. History of Holography. 2008. 25 Apr. 2009 <http://www.holography.ru/histeng.htm>.
6. ↑ ^{6.0 6.1 6.2 6.3} Thornton, Stephen T., and Andrew Rex. Modern Physics for Scientists and Engineers. Walnut Creek, CA: Brooks-Cole, 2006.
7. ↑ Outwater, Christopher., and Van Hamersveld. Practical Holography: The Laser. 2004. 20 Apr. 2009 <http://www.holo.com/holo//book/book.html#thlas>.
8. ↑ ^8.0 8.1 Outwater, Christopher., and Van Hamersveld. Practical Holography: Photon Emission. 2004. 20 Apr. 2009 <http://www.holo.com/holo//book/book.html#thlas>.
9. ↑ ^9.0 9.1 Wilson, Tracy V. HowStuffWorks.com: How Holograms Work. 21 May 2007. 26 April 2009. <http://science.howstuffworks.com/hologram.htm>
10. ↑ ^10.0 10.1 Nave, Carl R. HyperPhysics: Image on the Film of a Hologram. 2006. 18 Apr. 2009 <http://hyperphysics.phy-astr.gsu.edu/Hbase/optmod/holfilm.html#c1>.
11. ↑ ^{11.0 11.1 11.2} Outwater, Christopher., and Van Hamersveld. Practical Holography: The Basic Hologram Use. 2004. 20 Apr. 2009 <http://www.holo.com/holo//book/book.html#use>.
12. ↑ ^{12.0 12.1 12.2} Nave, Carl R. HyperPhysics: Viewing a Transmission Hologram. 2006. 18 Apr. 2009 <http://hyperphysics.phy-astr.gsu.edu/Hbase/optmod/holog2.html#c3>.
13. ↑ Nave, Carl R. HyperPhysics: When a piece is the whole. 2006. 18 Apr. 2009 <http://hyperphysics.phy-astr.gsu.edu/Hbase/optmod/holog.html#c4>.
14. ↑ ^14.0 14.1 Outwater, Christopher., and Van Hamersveld. Practical Holography: Movement Isolation. 2004. 20 Apr. 2009 <http://www.holo.com/holo//book/book.html#isol>.
15. ↑ Holography.co.uk. Types of Holograms. 8 Feb. 2008. 26 Apr. 2009 <http://www.holography.co.uk/questions/holtypes.htm>.
16. ↑ Holography Info. Types of Holograms. 23 Sep. 2007. 26 Apr. 2009 <http://holographyinfo.org/types.html>.
17. ↑ ^{17.0 17.1 17.2 17.3 17.4 17.5} 28 Apr. 2009 http://www.cdrinfo.com/sections/news/Details.aspx?NewsId=16013
18. ↑ 28 Apr. 2009 http://computers-thefinalfrontier.com/images/hvd-16.jpg
19. ↑ ^{19.0 19.1 19.2 19.3 19.4 19.5} 28 Apr. 2009 http://www.enterpriseitplanet.com/storage/features/article.php/3530796
20. ↑ 28 Apr. 2009 http://www.cnet.com.au/i/r/2005/CES%202006/holo_storage_sc.jpg
21. ↑ ^{21.0 21.1 21.2} 28 Apr. 2009 http://en.wikipedia.org/wiki/Holographic_Versatile_Disc
22. ↑ 28 Apr. 2009 http://www.youtube.com/watch?v=v7fQ_EsMJMs
23. ↑ Popfi.com. Image from Starwars. 20 Apr. 2009 <http://www.popfi.com/wp-content/uploads/star-wars-hologram.jpg>.