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Free-electron lasers as light sources for basic research

The free-electron laser (FEL) amplification mechanism is discussed, including the influence of the electron-beam quality (energy spread, emittance, stability) on the FEL performance. Considerations regarding the choice of the electron accelerator are presented, and some characteristic properties of the laser radiation are discussed. An overview of FEL-facilities for the infrared spectral region, which are being designed and built worldwide, is given.