Part 4

A possible solution is the use of “light pipes”, similar to the wave guides already in use for certain microwave applications over short distances. But as often happens, new developments create new needs; how, for example, can we get the laser beam to stay centered in the pipe and follow curves? A series of closely spaced lenses, about 1000 per mile, probably would accomplish this, but too much light would be lost by scattering from the many lens surfaces.

Scientists are experimenting with a new kind of “lens”, one that uses variations in the density of gases to focus and guide the beam automatically. Since there are no surfaces in the path of the light beam, and since the gas is transparent and free of turbulence, the laser beam is not appreciably weakened or scattered as it travels through the pipe.

Figure 31 shows how the gas focusing principle might be used to guide a beam through a curving pipe. The shading represents the density of the gas. Several means have been developed to keep the gas denser in the center than around the outside. When the pipe curves, the light beam starts moving off the axis of the pipe. The gas then acts like a prism, deflecting the light beam in the direction of the curvature of the “prism”.

In communication between distant space and earth, a light pipe might be a little cumbersome; hence it may prove necessary to set up an intermediate orbiting relay station that will, particularly in cases of poor weather, intercept the incoming laser beam and convert it to radio frequencies that can penetrate our atmosphere with greater reliability.

Powering space-borne lasers will, of course, be a problem. Indeed one of the major unsolved problems in production of spacecraft and long-term satellites is the provision of an adequate supply of power. Fuel cells and solar cells have helped but do not give the whole answer.[17]

One other approach has already been developed: a sun-pumped laser. Sunlight focused onto the side of the laser (see Figure 32) provides the pumping power, enabling the device to put out 1 watt of continuous infrared radiation, enough for special space applications. Descendents of this device could produce visible light if this is deemed desirable.

Another approach, using _chemical lasers_, is even more intriguing and may have greater consequences. Chemical lasers will derive their energy from their internal chemistry rather than from the outside. A mixture of two chemicals may be all that is needed to initiate laser action aboard a spacecraft or satellite. (Chemical lasers also offer the promise of even greater concentrations of power than have been achieved heretofore, which may make them useful in plasma research.)

With all these possibilities, it may still be that spacecraft will need more power than is available on board. The narrow beam of the laser offers one more fascinating possibility, especially in the case of satellites relatively near earth. The light of a laser might actually be used to beam energy to a receiver, either for immediate use or storage. It would then become possible to “refuel” satellites at will, giving them much greater capabilities.

If available laser power is great enough, laser beams might even be used to push satellites back into their proper orbits when they begin to wander off course, as they almost invariably do after a while.

Sun Parabolic Collector Hyperbolic-cylindric secondary mirror Semi-circular-cylindric tertiary mirror Laser beam

A LASER IN YOUR FUTURE?

Atomic energy, only a scientific dream a few short years ago, is now providing needed power in many parts of the world. In the same way, the laser, also an atomic phenomenon, has made its way out of the laboratory and into the fields of medicine, commerce, and industry. If it hasn’t touched your life as yet, you need only be patient. It will.

Indeed the most exciting probability of all is that lasers undoubtedly will change our lives in ways we cannot even conceive of now.

SUGGESTED REFERENCES

Books

_ABC’s of Masers and Lasers_, Allan H. Lytel, Howard W. Sams and Company, Inc., Publishers, Indianapolis, Indiana 46206, 1966, 96 pp., $2.25. _The Laser: Light That Never Was Before_, Ben Patrusky, Dodd, Mead and Company, New York 10016, 1966, 128 pp., $3.50. _Masers and Lasers_, Manfred Brotherton, McGraw-Hill Book Company, New York 10036, 1964, 224 pp., $8.50. _Masers and Lasers_, H. Arthur Klein, J. B. Lippincott Company, Philadelphia, Pennsylvania 19105, 1963, 184 pp., $3.95. _The Story of the Laser_, John M. Carroll, E. P. Dutton and Company, Inc., New York 10003, 1964, 181 pp., $3.95. _Quantum Electronics: The Fundamentals of Transistors and Lasers_, John R. Pierce, Doubleday and Company, Inc., New York 10017, 1966, 138 pp., $1.25. _Lasers and Their Applications_, Kurt R. Stehling, The World Publishing Company, Cleveland, Ohio 44102, 1966, 192 pp., $6.00. _Understanding Lasers and Masers_, Stanley Leinwoll, Hayden Book Companies, New York 10011, 1964, 96 pp., $1.95. _Atomic Light: Lasers_, Richard B. Nehrich, Jr., Glenn I. Voran, and Norman F. Dessel, Sterling Publishing Company, Inc., New York 10016, 1967, 136 pp., $3.95.

Articles—General and Historical

Advances in Optical Masers, A. L. Schawlow, _Scientific American_, 209: 34 (July 1963). The Evolution of the Physicist’s Picture of Matter, P. A. M. Dirac, _Scientific American_, 208: 45 (May 1963). Filling in the Blanks in the Laser’s Spectrum, F. M. Johnson, _Electronics_, 39: 82 (April 18, 1966). The Amateur Scientist—How a persevering amateur can build a gas laser in the home, C. L. Stong, _Scientific American_, 211: 227 (September 1964). The Amateur Scientist—Homemade Laser, C. L. Stong, _Scientific American_, 213: 108 (December 1965). The Amateur Scientist—How to make holograms and experiment with them or with ready-made holograms, C. L. Stong, _Scientific American_, 216: 122 (February 1967). The Maser, James P. Gordon, _Scientific American_, 199: 42 (December 1958). The Quantum Theory: Early Years to 1923, Karl Darrow, _Scientific American_, 186: 47 (March 1952). Laser’s Bright Magic, T. Meloy, _National Geographic Magazine_, 130: 858 (December 1966). Infrared and Optical Masers (original paper), A. L. Schawlow and C. H. Townes, _Physical Review_, 112: 1940 (December 15, 1958). Laser Market Enters Era of Practicality, W. Mathews, _Electronic News_, 11: 1 (April 18, 1966). Lasers, A. K. Levine, _American Scientist_, 51: 14 (March 1963). Lasers, A. L. Schawlow, _Science_, 149: 13 (July 2, 1965). Lasers and Coherent Light, A. L. Schawlow, _Physics Today_, 17: 28 (January 1964). The Laser’s Dazzling Future, L. Lessing, _Fortune_, 67: 138 (June 1963). Optical Masers, A. L. Schawlow, _Scientific American_, 204: 52 (June 1961). Optical Pumping, A. L. Bloom, _Scientific American_, 202: 72 (October 1960). Research on Maser-Laser Principle Wins Nobel Prize in Physics, J. P. Gordon, _Science_, 146: 897 (November 13, 1964). Resource Letter MOP-1 on Masers (Microwave through Optical) and on Optical Pumping, H. W. Moos, _American Journal of Physics_, 32: 589 (August 1964), extensive bibliography. Available from American Institute of Physics, 335 East 45th Street, New York 10017. Enclose stamped return envelope. Advances in Holography, K. S. Pennington, _Scientific American_, 218: 40 (February 1968). Applications of Laser Light, D. R. Herriott, _Scientific American_, 219: 140 (September 1968). Holography for the Sophomore Laboratory, R. H. Webb, _American Journal of Physics_, 36: 62 (January 1968). Laser Light, A. L. Schawlow, _Scientific American_, 219: 120 (September 1968). The Modulation of Laser Light, D. F. Nelson, _Scientific American_, 218: 17 (June 1968).

Articles—Special Subjects

Biological Effects of High Peak Power Radiation, S. Fine et al., _Life Sciences_, 3: 209 (1964). The Interaction of Light with Light, J. A. Giordmaine, _Scientific American_, 210: 38 (April 1964). Chemical Lasers, George C. Pimental, _Scientific American_, 214: 32 (April 1966). Color Laser Stores Data, J. Eberhart, _Science News_, 90: 51 (July 23, 1966). Communication by Laser, Stewart E. Miller, _Scientific American_, 214: 19 (January 1966). Guidelines for Selecting Laser Materials, R. H. Hoskins, _Electronic Design_, 13: _M_29 (July 19, 1965). Holography: The Picture Looks Good, J. Blum, _Electronics_, 39: 139 (April 18, 1966). How Dangerous Are Lasers?, L. H. Dulberger, _Electronics_, 35: 27 (January 26, 1962). Injection Lasers, R. W. Keyes, _Industrial Research_, 6: 46 (October 1964). Laser Potential in Deep-Space Link Grows, B. Miller, _Aviation Week and Space Technology_, 84: 71 (January 31, 1966). Laser Retinal Photocoagulator, N. S. Kapany et al., _Applied Optics_, 4: 517 (May 1965). Laser Welding in Electronic Circuit Fabrication, J. P. Epperson, _Electrical Design News_ (EDN), 10: 8 (October 1965). The Light That Slices Inch into Millionths, (use of interferometry in industry), _Steel_, 158: 38 (February 28, 1966). The Optical Heterodyne—Key to Advanced Space Signaling, S. Jacobs, _Electronics_, 36: 29 (July 12, 1963). Photography by Laser, E. N. Leith and J. Upatnieks, _Scientific American_, 212: 24 (June 1965). Liquid Lasers, Alexander Lempicki and Harold Samelson, _Scientific American_, 216: 81 (June 1967). Plasma Experiments with a 570-kJ Theta-Pinch, F. C. Yahoda, et al., _Journal of Applied Physics_, 35: 2351 (August 1964). A Sun-Pumped CW One-Watt Laser, C. G. Young, _Applied Optics_, 5: 993 (June 1966). 3-D Image Made at Home, _Science News_, 90: 185 (10 September 1966). Scanning with Lasers, Robert A. Myers, _International Science and Technology_, 65: 40 (May 1967).

Booklets

_Applications of Lasers to Information Handling_, The Perkin-Elmer Corporation, Norwalk, Connecticut 06852, 1966, 32 pp., free. Reprint of five talks given by company personnel. _Laser Interferometer_, Airborne Instruments Laboratory, Division of Cutler-Hammer, Inc., Deer Park, Long Island, New York 11729, 1965, 20 pp., free. Collection of article reprints. _Laser: The New Light_, Bell Telephone Laboratories, Murray Hill, New Jersey 07971, 19 pp., free. Full color, nontechnical brochure presents some background, principles, and applications of the laser.

FOOTNOTES

[1]Sometimes referred to as _hertz_ (abbreviated Hz), for the 19th Century German physicist Heinrich Hertz; 1000 Hz = 1000 cps.

[2]Devised in France and officially adopted there in 1799, the metric system uses the meter as the basic unit of length and has been proposed for all measurements in this country.

[3]Named for the Swedish physicist Anders J. Angstrom.

[4]The wavelength, indicated by the Greek letter λ (lambda) is related to frequency (f) in the proportion λ (in meters) = 300,000,000/f. (The number 300,000,000 is the velocity of light in meters per second.)

[5]Microwaves are radio waves with frequencies above 1000 megacycles per second.

[6]Ten to 30,000,000 kilocycles per second; this is low in the electromagnetic spectrum, but not low in terms of the radio spectrum, which has a low-frequency classification of its own.

[7]Primitive as early radios were by today’s standards, they brought a new era to communication at the time. Unmodulated CW (continuous wave) transmissions and crystal receivers were used to summon rescuers in the _Titanic_ disaster of 1912, for example.

[8]Energy = h (Planck’s constant) × frequency. Planck’s constant is the energy of 1 quantum of radiation, and equals 6.62556 × 10⁻²⁷ erg-sec.

[9]Each photon carries 1 _quantum_ of radiation energy, which is a unit equal to the product of the radiation frequency and Planck’s constant (see footnote page 15).

[10]Einstein was awarded the Nobel Prize in 1921 for his 1905 explanation of the photoelectric effect (in terms of quanta of energy) and _not_ for his relativity theory.

[11]Einstein’s theoretical explanation applies in the case of stimulation of a single atom. In practical stimulation, directionality is enhanced by stimulating many atoms in phase.

[12]An atomic clock is a device that uses the extremely fast vibrations of molecules or atomic nuclei to measure time. These vibrations remain constant with time, consequently short intervals can be measured with much higher precision than by mechanical or electrical clocks.

[13]The 1966 Nobel Prize in Physics was awarded to Prof. Alfred Kastler of the University of Paris for his research on optical pumping and studies on the energy levels of atoms.

[14]See _Accelerators_, a companion booklet in this series, for a full account of the Stanford “Atom Smasher”.

[15]For descriptions of fission and fusion processes, see _Controlled Nuclear Fusion_, _Nuclear Reactors_, and _Nuclear Power Plants_, other booklets in this series.

[16]A bit is a digit, or unit of information, in the binary (base-of-two) system used in electronic data transmission systems.

[17]See _SNAP_, _Nuclear Space Reactors_ and _Power from Radioisotopes_, other booklets in this series, for descriptions of nuclear sources of power for space.

This booklet is one of the “Understanding the Atom” Series. Comments are invited on this booklet and others in the series; please send them to the Division of Technical Information, U. S. Atomic Energy Commission, Washington, D. C. 20545.

Published as part of the AEC’s educational assistance program, the series includes these titles:

_Accelerators_ _Animals in Atomic Research_ _Atomic Fuel_ _Atomic Power Safety_ _Atoms at the Science Fair_ _Atoms in Agriculture_ _Atoms, Nature, and Man_ _Books on Atomic Energy for Adults and Children_ _Careers in Atomic Energy_ _Computers_ _Controlled Nuclear Fusion_ _Cryogenics, The Uncommon Cold_ _Direct Conversion of Energy_ _Fallout From Nuclear Tests_ _Food Preservation by Irradiation_ _Genetic Effects of Radiation_ _Index to the UAS Series_ _Lasers_ _Microstructure of Matter_ _Neutron Activation Analysis_ _Nondestructive Testing_ _Nuclear Clocks_ _Nuclear Energy for Desalting_ _Nuclear Power and Merchant Shipping_ _Nuclear Power Plants_ _Nuclear Propulsion for Space_ _Nuclear Reactors_ _Nuclear Terms, A Brief Glossary_ _Our Atomic World_ _Plowshare_ _Plutonium_ _Power from Radioisotopes_ _Power Reactors in Small Packages_ _Radioactive Wastes_ _Radioisotopes and Life Processes_ _Radioisotopes in Industry_ _Radioisotopes in Medicine_ _Rare Earths_ _Research Reactors_ _SNAP, Nuclear Space Reactors_ _Sources of Nuclear Fuel_ _Space Radiation_ _Spectroscopy_ _Synthetic Transuranium Elements_ _The Atom and the Ocean_ _The Chemistry of the Noble Gases_ _The Elusive Neutrino_ _The First Reactor_ _The Natural Radiation Environment_ _Whole Body Counters_ _Your Body and Radiation_

A single copy of any one booklet, or of no more than three different booklets, may be obtained free by writing to:

USAEC, P. O. BOX 62, OAK RIDGE, TENNESSEE 37830

Complete sets of the series are available to school and public librarians, and to teachers who can make them available for reference or for use by groups. Requests should be made on school or library letterheads and indicate the proposed use.

Students and teachers who need other material on specific aspects of nuclear science, or references to other reading material, may also write to the Oak Ridge address. Requests should state the topic of interest exactly, and the use intended.

In all requests, include “Zip Code” in return address.

Printed in the United States of America USAEC Division of Technical Information Extension, Oak Ridge, Tennessee

Transcriber’s Notes

—Silently corrected a few typos.

—Retained publication information from the printed edition: this eBook is public-domain in the country of publication.

—In the text versions only, text in italics is delimited by _underscores_.