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1 - Electromagnetic waves, light, and lasers

Published online by Cambridge University Press:  05 June 2014

Christopher C. Davis
Christopher C. Davis
Affiliation:
University of Maryland, College Park
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Summary

The laser

A laser is an oscillator that operates at optical frequencies. These frequencies of operation lie within a spectral region that extends from the very far infrared to the vacuumultraviolet (VUV) or soft-X-ray region. At the lowest frequencies at which they operate, lasers overlap with the frequency coverage of masers, to which they are closely related, and millimeter-wave sources using solid-state or vacuum-tube electronics, such as TRAPATT, IMPATT, and Gunn diodes, klystrons, gyroklystrons, and traveling-wave tube oscillators, whose principles of operation are quite different [1]. In common with electronic-circuit oscillators, a laser is constructed using an amplifier with an appropriate amount of positive feedback. The positive feedback is generally provided by mirrors that re-direct light back and forth through the laser amplifier. The acronym LASER, which stands for light amplification by stimulated emission of radiation, is in reality therefore a slight misnomer.

A little bit of history

The basic physics underlying light emission and absorption by atoms and molecules was first expounded by Albert Einstein (1879–1955) in 1917 [2]. Richard Chace Tolman (1881–1948) observed that stimulated emission could lead to “negative absorption.” In 1928 Rudolph Walther Landenburg (1889–1953) confirmed the existence of stimulated emission and negative absorption. It is interesting to note that a famous spectroscopist, Curtis J. Humphreys (1898–1986), who for most of his career worked at the U.S. Naval Ordnance Laboratory in Corona, California, might have operated the first gas laser without knowing it.

Type
Chapter
Information
Lasers and Electro-optics
Fundamentals and Engineering
 , pp. 1 - 32
Publisher: Cambridge University Press
Print publication year: 2014

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References

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