Margaret M. Loos
Three new and often interlocking technologies of light with tremendous potential are LASERS, FIBER OPTICS and HOLOGRAPHY. Light brings us energy in a diffuse state. All the frequencies of the electromagnetic spectrum are jumbled together causing overlapping and interference. Einstein predicted forty-five years before the first laser that such a device could be made. He said that if electrons within an atom were excited (by infusion of energy) and were struck by an emitted photon, that excited electron would drop down to a lower energy level, and emit a photon in the same phase and moving in the same direction. These photons are now considered as having no mass, but behaving like particles. These photons released are now sent out in only one frequency, and the waves are positively reinforced. Thus, the laser (Light Amplification by Stimulated Emission of Radiation) acronym.
The atom, which has been taught in both the courses this unit pertains to, has its electrons arranged in a definite pattern of shells. The arrangement is that which requires the least energy, and therefore is the most stable. When the electrons are excited by an energy source these electrons may jump to a higher shell. They immediately release their new energy as photons and drop back down to that
ground
state
.
The first successful laser was a ruby crystal with mirrored ends. Actually impurities of chromium make a ruby, which is aluminum oxide, take on its deep red color. A flash lamp provided light energy to be absorbed and thus the chromium atoms were excited. When the excited electrons within these atoms returned to their ground state, the emitted photons struck the mirrors, were reflected to strike more atoms, and thus the numbers were multiplied and the radiation was amplified. The radiation eventually became so intense that when it finally “escaped” it was an unbelievably pure ruby light. The scientist who first accomplished this breakthrough in light technology was Theodore H. Maimon, in the year 1960.
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The steps in the action of any laser are:
1. Atoms are excited.
2. Photons are emitted.
3. They are reflected back and forth.
4. A powerful beam is emitted.
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(figure available in print form)
Perhaps the most common laser the students encounter is the helium neon laser in the checkout counters at the supermarket which “reads” prices.
All laser lights are intense, directed and pure. The media may be crystals, glass, gases or liquids. The energy sources may be high intensity light, electricity, or nuclear radiation. The range of the frequencies has been extended from microwaves through the visible spectrum to ultraviolet and x-rays. Lasers can concentrate great power, equal to millions of watts and can also produce great heat. They are harnessing light, a basic form of energy, and they are the basis of a revolution in the use of energy. They can be directed very precisely. Their characteristics and their range of frequencies enable their use for such wide spread operations as bloodless surgery, precise and rapid measurement, tremendous strides in communication, even the ability to probe the ocean and the atmosphere. Unfortunately. their potential for warfare and military expansion is awesome.
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FIBER
OPTICS
: Lasers are used as the transmitters in another new technology, or tool of light, fiber optics. Fiber optics are also referred to as lightwave transmission. The glass is the clearest in the world free of almost all impurities. The fiber is densest in the middle, and less dense on the outside. This area (outside) is called cladding. The sides of the fiber reflect the light and keep it inside even as the fiber twists and bends, thereby giving total internal reflection. The light sources are usually very small lasers that flash on and off sending messages. The frequencies of the light usually used are in the infrared range.
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Fiber optics are being used in communications (phones particularly) and medical photography (endoscopy), for connecting computers, video-telephones (Japan) and television and holography.
HOLOGRAPHY
: Holography is the production of three dimensional photographs. The word holograph means “Whole message.” Holography can actually work with any waves. First developed by Dennis Gabor to improve the electron microscope, the electron beams probe in all directions on an object getting all the information. This complete pattern it produces could be called a wave front but it produces no image or picture. However, when this wave front intersects with a second set of light rays—a reference beam—the wave front can be recorded and later reconstructed by the proper illumination. When we see it from the right angle we see the entire object.
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ACTIVITIES
: Find Science World articles in last year’s issues on these new technologies.
Viewing a light show if possible
Display of holograms
See fiber optics’ transmission of light with fiber optic samples