The Airborne Laser from Theory to Reality: An Insider's Account

By Mark, Hans | Defense Horizons, April 2002 | Go to article overview

The Airborne Laser from Theory to Reality: An Insider's Account


Mark, Hans, Defense Horizons


Introduction and Scientific Background

Albert Einstein spent World War I in Berlin, where he developed a theory that described electromagnetic radiation in equilibrium with atoms that could emit and absorb radiation. The innovation in Einstein's work, which was published in 1916 and 1917, was that he used the newly developed quantum theory to obtain his results. The most important result was not only that the atoms in the assembly could absorb and emit radiation spontaneously but also that atoms in certain excited states could be induced to emit radiation. (1) Einstein called this discovery the stimulated emission of radiation. Einstein's discovery provided the basis for the development of lasers, though the phenomenon would not be observed in the laboratory for many years.

The development of radar during World War II required intensive research in microwave radiation. The need for highly sensitive radar receivers led to isolating and observing for the first time Einstein's stimulated emission of radiation. In 1954, Charles H. Townes, J.P. Gordon, and H.J. Zeiger were the first to amplify a microwave signal by using stimulated emission. (2) They called their device the maser, which stood for Microwave Amplification by the Stimulated Emission of Radiation. This work led many to speculate about applying the same principles to radiation in other regions of the electromagnetic spectrum. This effort turned out to be successful, and 6 years later, a positive result was achieved with visible light.

The first laser (Light Amplification by the Stimulated Emission of Radiation) was developed by Theodore H. Maiman in 1960 at the Hughes Aircraft Corporation research laboratory. (3) To develop the laser, a material had to be found in which an assembly of atoms, most of which were in a higher energy state than the ground state (or lowest energy state) of the atom, could be created. Such a condition is called a population inversion. Where it exists, a light pulse can be amplified by stimulating the emission of radiation by the atoms in the higher energy state. Thus, a strong light pulse can be obtained using a small stimulus--hence the term amplification. Maiman found that a population inversion could be produced within certain atoms in an appropriately designed ruby rod by irradiating it with a strong pulse of light. The atoms in the higher energy states could be stimulated to emit radiation by a very weak light signal of the proper frequency, which would create a cascade that would stimulate the emission of light by all other atoms in the higher energy state, producing a strong pulse of red light.

About the same time, Ali Javan and his collaborators at Bell Laboratories discovered a way to create a population inversion in a mixture of helium, neon, and other gases. (4) The tube in which these gases were placed was irradiated continuously with light of the appropriate wavelength. A population inversion was created in the gas mixture, which created a tightly focused beam at a sharply defined wavelength. This tight focus bore out Einstein's 1916-1917 prediction. His calculations revealed that the light quanta or photons created by the stimulated emission are in exactly the same quantum state as the photon that initiated the stimulated emission. This means that all the photons in the process are moving in exactly the same direction, thus creating the tightly focused beam.

Solid-state and gas lasers of the type described here are limited in terms of the energy that the laser beam contains because the population inversion is eventually destroyed by melting or other change in the state of the medium in which it is created. The best continuous energy both in pulsed and continuous wave beams is of the order of kilowatts. Lasers of this kind are useful for many purposes, including meteorology, bar-code scanning, and target designation. One of the most fascinating applications of a solid-state laser with energy in the kilowatt range is the lunar laser ranging experiment conducted for the past 30 years at the University of Texas McDonald Observatory.

The rest of this article is only available to active members of Questia

Sign up now for a free, 1-day trial and receive full access to:

  • Questia's entire collection
  • Automatic bibliography creation
  • More helpful research tools like notes, citations, and highlights
  • Ad-free environment

Already a member? Log in now.

Notes for this article

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
One moment ...
Project items

Items saved from this article

This article has been saved
Highlights (0)
Some of your highlights are legacy items.

Highlights saved before July 30, 2012 will not be displayed on their respective source pages.

You can easily re-create the highlights by opening the book page or article, selecting the text, and clicking “Highlight.”

Citations (0)
Some of your citations are legacy items.

Any citation created before July 30, 2012 will labeled as a “Cited page.” New citations will be saved as cited passages, pages or articles.

We also added the ability to view new citations from your projects or the book or article where you created them.

Notes (0)
Bookmarks (0)

You have no saved items from this article

Project items include:
  • Saved book/article
  • Highlights
  • Quotes/citations
  • Notes
  • Bookmarks
Notes
Cite this article

Cited article

Style
Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

(Einhorn, 1992, p. 25)

(Einhorn 25)

1

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited article

The Airborne Laser from Theory to Reality: An Insider's Account
Settings

Settings

Typeface
Text size Smaller Larger
Search within

Search within this article

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

Full screen

matching results for page

Cited passage

Style
Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn, 1992, p. 25).

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences."1

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited passage

Welcome to the new Questia Reader

The Questia Reader has been updated to provide you with an even better online reading experience.  It is now 100% Responsive, which means you can read our books and articles on any sized device you wish.  All of your favorite tools like notes, highlights, and citations are still here, but the way you select text has been updated to be easier to use, especially on touchscreen devices.  Here's how:

1. Click or tap the first word you want to select.
2. Click or tap the last word you want to select.

OK, got it!

Thanks for trying Questia!

Please continue trying out our research tools, but please note, full functionality is available only to our active members.

Your work will be lost once you leave this Web page.

For full access in an ad-free environment, sign up now for a FREE, 1-day trial.

Already a member? Log in now.