What is hologram
- meaning of hologram
- rainbow hologram
- making hologram
- how hologram works
- application holograms
- who invented holograms
- future of hologram technology
A hologram is a three-dimensional image, created with photographic projection. The term is taken from the Greek words holos (whole) and gramma (message). Unlike 3-D or virtual reality on a two-dimensional computer display, a hologram is a truly three-dimensional and free-standing image that does not simulate spatial depth or require a special viewing device. Theoretically, holograms could someday be transmitted electronically to a special display device in your home and business.
A hologram is an image created by a photographic projection of a recording of a light field rather than an image formed by some sort of lens. It appears as a three-dimensional representation on a two-dimensional object, which can be seen without intermediate optics such as goggles or glasses. However these hologram images become unintelligible when viewed under diffused ambient light since they are not actual images. The photographic technique used to create these images is called holography.
Techopedia explains Hologram
Hologram refers to both the physical medium that diffracts the light to create the image and the resulting image itself. The first practical optical hologram that recorded a 3-D object was invented in 1962 by Yuri Denisyuk of the then Soviet Union and by Dennis Leith and Juris Upatnieks at the University of Michigan. Since its development in 1962, various hologram types have been developed.
One type is called a transmission hologram. These holograms are produced by splitting the laser light into an illumination beam and a reference beam. The illumination beam is projected directly on the object while the reference beam is projected directly onto the photographic medium, forming an interference pattern on the film; the result is a captured light field that was taken in a method similar to traditional photography processes.
Another type of hologram is the rainbow hologram, which is commonly used for authentication and security purposes. These are designed to be viewable under the illumination of white light rather than laser light like other types of holograms. The image is created using a vertical slit which removes vertical parallax in the resulting image, reduces spectral blur and preserves the three-dimensionality for most observers. These can usually be found on credit cards, product packaging and driver’s licenses.
Another common type is the Denisyuk hologram or reflection hologram. This type is seen in holographic displays and is capable of multicolor image reproduction.
You make a hologram by reflecting a laser beam off the object you want to capture. In fact, you split the laser beam into two separate halves by shining it through a half-mirror (a piece of glass coated with a thin layer of silver so half the laser light is reflected and half passes through—sometimes called a semi-silvered mirror). One half of the beam bounces off a mirror, hits the object, and reflects onto the photographic plate inside which the hologram will be created. This is called the object beam. The other half of the beam bounces off another mirror and hits the same photographic plate. This is called the reference beam. A hologram forms where the two beams meet up in the plate.
Laser light is much purer than the ordinary light in a flashlight (torch) beam. In a flashlight beam, all the light waves are random and jumbled up. Light in a flashlight beam runs along any old how, like schoolchildren racing down a corridor when the bell goes for home time. But in a laser, the light waves are coherent: they all travel precisely in step, like soldiers marching on parade.
When a laser beam is split up to make a hologram, the light waves in the two parts of the beam are traveling in identical ways. When they recombine in the photographic plate, the object beam has traveled via a slightly different path and its light rays have been disturbed by reflecting off the outer surface of the object. Since the beams were originally joined together and perfectly in step, recombining the beams shows how the light rays in the object beam have been changed compared to the reference beam. In other words, by joining the two beams back together and comparing them, you can see how the object changes light rays falling onto it—and that's simply another way of saying "what the object looks like." This information is burned permanently into the photographic plate by the laser beams. So a hologram is effectively a permanent record of what something looks like seen from any angle.
Now this is the clever part. Every point in a hologram catches light waves that travel from every point in the object. That means wherever you look at a hologram you see exactly how light would have arrived at that point if you'd been looking at the real object. So, as you move your head around, the holographic image appears to change just as the image of a real object changes. And that's why holograms appear to be three-dimensional. Also, and this is really neat, if you break a hologram into tiny pieces, you can still see the entire object in any of the pieces: smash a glass hologram of a cup into bits and you can still see the entire cup in any of the bits! (You can see a demonstration in this great video of cutting up a hologram and Hyperphysics has a more detailed explanation of exactly what we mean when we say "a piece of a hologram contains the whole object".)
Until the 1980s, holograms were a slightly wacky scientific idea. Then someone found a way of printing them onto metallic film and they became an incredibly important form of security. Proper glass holograms look much more impressive than the tiny metallic ones you see on banknotes and credit cards and you often see them used in jewelry or other decorative items: you can even have holographic pictures hanging on your wall with eyes that really do follow you around the room! In the 1980s, a British theater even projected a hologram of Laurence Olivier on stage to save the actor (who was, by then, quite elderly) the hassle of appearing in person each night. Lots of artists have experimented with making holographic pictures, including the Spanish surrealist Salvador Dali. Holograms also have important medical and scientific uses. In a technique called holographic interferometry, scientists can make a hologram of something like an engine part and store it as a "three-dimensional photograph" for later reference. If they make another hologram of the engine part at some later date, comparing the two holograms quickly shows up any changes in the engine that may indicate signs of wear or impending failure.
No-one's yet found a good way of making moving pictures with holograms, but it's probably only a matter of time. Once that happens, we can look forward to three-dimensional holographic TV and a whole new era of super-realistic entertainment!
Dennis Gabor's original sketch of his 1950s holographic apparatus. Monochromatic light (yellow) enters at the bottom (1), passes through various prisms (blue) and lenses (gray) and is split into two beams. The low-intensity object beam on the left passes through the specimen on a slide (red, 10); the high intensity reference beam on the right continues in parallel without touching the specimen. The beams are recombined in a photographic plate (21/22) at the top after passing through more lenses (gray) and prisms (blue). Artwork from US Patent #2,770,166: Improvements in and relating to optical apparatus for producing multiple interference patterns by Dennis Gabor, courtesy of US Patent and Trademark Office.
Holograms were invented by a brilliant Hungarian-born physicist named Dennis Gabor (1900–1979) while he was working in the UK. He'd been researching optical physics in the 1940s, and carried out his breakthrough work in holography in the early 1950s. The remarkable thing about his invention is that it was many years ahead of its time: lasers, which made holography practical, did not appear until the 1960s. As Gabor's many patents show, he was a prolific inventor with wide-ranging interests across many different areas of physics. In the 1930s, he invented new kinds of electron multipliers and cathode-ray tubes; in the 1940s, he was experimenting with photography and projection, which set him on the road toward holography; later inventions included composite fabrics for use in television equipment, and various innovations in recording and transmitting sound. Towards the end of his life, Gabor's brilliant contribution was recognized by the award of the world's top science prize, the Nobel Prize in Physics 1971, "for his invention and development of the holographic method.
Raw Materials for making hologram
Holograms made by individuals are usually exposed on very high resolution photographic film coated with a silver halide emulsion. Holograms made for mass production are exposed on a glass plate pretreated with iron oxide and then coated with photoresist. The photoresist material will chemically react to the specific wavelength of light that will be used to create the hologram. Because of their availability at a relatively low cost, helium-neon lasers are most commonly used by individuals who make their own holograms. Commercial hologram manufacturers use different laser types such as ruby, helium-cadmium, or krypton-argon ion.
After exposure, the film or photoresist plate is processed in chemical developers like those used in photography. Both nickel and silver are used to make the production masters that will be used to stamp multiple copies of the holograms onto polyester or polypropylene film. Aluminum is used to create the reflective coating on the back of embossed holograms.
Design of a hologram
A three-dimensional, physical object can be used to create a hologram. The holographic image is normally the same size as the original
object. This may require construction of a detailed scale model of the actual subject in a size suitable for the holographic image. Altematively, the artwork that is to be reproduced as a hologram can be computer generated, in which case software controls the laser exposure of the image file, one pixel at a time. (Pixels are the individual dots that comprise a graphic image on a computer screen or printout.)
Various manuals are available that explain to amateur holographers how to make holograms at home. The following steps describe the commercial mass production of a holographic image of an actual, three-dimensional object.
- A laser is used to illuminate the physical object, with the reflected light falling on the photoresist plate. Simultaneously, a reference beam from the laser also falls directly on the photoresist plate. The interference patterns of these two light beams react with the photo-sensitive coating to record a holographic image of the object. Common exposure times are between one to 60 seconds. In photography, slight motion of the object or the film results in a blurred image. In holography, however, the exposed plate will be blank (contain no image at all) if during the exposure there is movement as small as one fourth the wavelength of the laser light (wavelengths of visible light range from 400 to 700 billionths of a meter).
A typical photoresist plate has a 6 in (15.24 cm) square working area; an extra half-inch (1.25 cm) of space on two edges allows the plate to be clamped into position. Because many holograms are smaller than this, several different images can be "ganged" (clustered) onto one plate, just as numerous individual photographs are exposed on one roll of film.
- The plate on which the original hologram is recorded is called the master. After being exposed, the master is processed in a chemical bath using standard photographic developers. Before proceeding with production, the master is inspected to confirm that the image has been properly recorded. Because of the chemical reactions caused by the laser and the developer on the photoresist, the developed plate's surface resembles the surface of a phonograph record; there are about 15,000 grooves per inch (600 per cm), reaching a depth of about 0.3 microns (1 micron is a thousandth of a millimeter).
- The master is mounted into a jig (frame) and sprayed with silver paint to achieve good electrical conductivity. The jig is lowered into a tank along with a supply of nickel. An electric current is introduced, and the master is electroplated with nickel. The jig is removed from the tank and washed wit
deionized water. The thin, nickel coating, which is called the metal master shim, is peeled off the master plate. It contains a negative image of the master hologram (the negative is actually a mirror image of the original hologram).
Using similar processes, several generations of shims are created. Those made from the metal master shim are known as "grandmothers," and they contain positive images of the original hologram. At this stage, numerous copies of the original image are "combined" (duplicated in rows) on one shim that can be used to print multiple copies with a single impression. Successive generations of shims are known as "mothers," "daughters," and "stamper shims." Because these generations alternate between negative and positive images of the original, the stamper shims are negative images that will be used during actual production runs to print the final product holograms.
- Stamper shims are mounted in embossing machines. A roll of polyester film (or a similar material) that has been smoothed with an acrylic coating is run through the machine. Under intense heat and pressure, the shim presses the holographic image onto the film, to a depth of 25 millionths of a millimeter. The embossed film is rewound onto a roll.
- The roll of embossed film is loaded into a chamber from which the air is removed to create a vacuum. The chamber also contains aluminum wire, which is vaporized by heating it to 2,000°F (1,093°C). The sheet is exposed to the vaporized aluminum as it is rewound onto another roll, and in the process it becomes coated with aluminum. After being removed from the vacuum chamber, the film is treated to restore moisture lost under the hot vacuum condition. A top coating of lacquer is applied to the film to create a surface that can be imprinted with ink. The roll of film, which may be as wide as 92 in (2.3 m), is sliced into narrower rolls.
• 6 Depending on what type of film was used and what kind of product is being made, one or more finishing steps may be done. For instance, the film may be laminated to paper board to give it strength. The film is also cut into shapes desired for the final product and may be printed with messages. Heat-sensitive or pressure-sensitive adhesive is applied to the back of holograms that will be affixed to other objects or used as stickers.
- The holograms are either attached to other products or are counted and packaged for shipment.
Today, the most common use of holograms is in consumer products and advertising materials. There are some unusual applications too. For example, in some military aircraft, pilots can read their instruments while looking through the windshield by using a holographic display projected in front of their eyes. Automobile manufacturers are considering similar displays for their cars.
Holograms can be created without visible light. Ultraviolet, x-ray, and sound waves can all be used to create them. Microwave holography is being used in astronomy to record radio waves from deep space. Acoustical holography can look through solid objects to record images, much as ultrasound is used to generate images of a fetus within a woman's womb. Holograms made with short waves such as x rays can create images of particles as small as molecules and atoms.
Holographic television sets may project performers into viewers' homes within the next decade. Fiber optic communications systems will be able to transmit holographic images of people to distant homes of friends for realistic visits. Just as CD-ROM technology used optical methods to store large amounts of computer information on a relatively small disk, three-dimensional holographic data storage systems will further revolutionize storage capacities. It is estimated that this technology will store an amount of information equivalent to the contents of the Library of Congress in a space the size of a sugar cube.