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The Free Electron Laser
| Article
# : |
16034 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
7 / 1989 |
2,530 Words |
| Author
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C.W. Roberson
C.W. Roberson is a scientific officer at the Office of Naval
Research. He is co-author with P. Sprangle of "A Review of
Free Electron Lasers," published in Physics of Fluids B
(Plasma Physics), Vol.1 No. 1, pages 3-42, 1989. |
The free electron laser (FEL) is a device that converts the energy of an electron beam to coherent radiation by passing it through a periodic magnetic field. The primary advantage of the free electron laser over other lasers is that it can be tuned to produce radiation over a very wide range of wavelengths. The free electron laser is also capable of very high-power operation. There advantages and recent development in electron sources, electron accelerators, and magnet technology have made the free electron laser a potential alternative source of coherent radiation across the ultraviolet, visible, infrared, and microwave regions of the electromagnetic spectrum.
For the past 30 years the laser has operated at the relatively few wavelengths for which appropriate atomic and molecular transitions exist. During this period it has revived the field of optics and been employed in a variety of unique applications. However, the FEL's tenability and range of wavelength operation may make it the only coherent source at many wavelengths.
Potential FEL applications are apparent in many different areas, including energy generation by using high-power microwave radiation to heat plasmas to thermonuclear fusion temperatures; missile defense by using high-power radiation in the optical wavelengths for SDI directed energy weapons applications; and in the laser separation of isotopes of uranium.
At infrared and submillimeter microwave wavelengths where few other coherent sources exist, the free electron laser provides many unique opportunities, such as the excitation of collective modes in solids or new radar sources. The FEL also provides a source of tunable radiation, corresponding to the band gap in semiconductors that could lead to new transistors. In applications in biological systems the free electron laser may be tunable through resonances that play a part in enzyme reactions for the unwinding of DNA. The FEL's tenability has also made it an attractive candidate for diverse applications in laser medicine where its wide range of frequencies offers the possibility of selectively cutting bone, fatty tissue, or cancerous tumors. At ultraviolet wavelength, the free electron laser offers a unique opportunity for improvements in the lithography of submicron electronics.
The FEL Mechanism
The free electron laser is a classical device; that is, it does not rely on the quantum mechanical radiation processes that are fundamental to the operation of
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