Free Electron Lasers and Other Advanced Sources of Light Scientific Research Opportunities (1994) / Chapter Skim
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2 THE FREE ELECTRON LASER
2 THE FREE ELECTRON LASER
Pages 16-23
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From page 16... ...
Two important FEL attributes, tunability and design flexibility, were demonstrated by these two experiments at significantly different wavelengths using the same apparatus. r ~ PRINCIPLES OF OPERATION In an FEL a beam of relativistic electrons produced by an electron accelerator passes through a transverse, periodic magnetic field produced by a magnet called an undulator and exchanges energy with an electromagnetic radiation field.
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From page 17... ...
The radiation pulse structure in an FEL reflects that of the electron beam. resonator FIGURE 7 Schematic of a free electron laser.
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From page 18... ...
The FEL is able to obtain large peak power, on the order of a few gigawatts, because, unlike conventional lasers or microwave tubes, the energy that is not transferred to the radiation field remains in the relativistic electron beam that is transported out of the undulator at nearly the speed of light, or even recovered to improve overall efficiency. The FEL interaction volume contains only light, the undulator magnetic field, and the electron beam, so that unwanted high field effects and thermal distortion of the medium are absent in the FEL.
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From page 19... ...
Because the FEL uses ~ single gain medium, the relativistic electron beam, and because the resonant condition can be easily tuned by changing either the electron beam energy or the magnetic field strength, FELs are broadly and easily tuned. A factor-of-LO tunable frequency range has already been demonstrated with the same accelerator and undulator.
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From page 20... ...
FELs can have significant emission at harmonics of the fundamental frequency given by the resonance condition, and harmonics can be used to extend operation to shorter wavelengths than would be practical using only the fundamental frequency. At present, the shortest wavelength that has been achieved in an FEL is 240 nm, and significant use of FELs for scientific research has been restricted to the infrared.
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From page 21... ...
1982. The Free Electron Laser.
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From page 23... ...
E Johnson, The Brookhaven National Laboratory DUV Free Electron Laser Report, January 1994.
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