Long wavelength free-electron lasers in 1998

A summary of the current status and most important future directions for lo ng wavelength (greater than or equal to 0.5 mm) free-electron lasers is pre sented. The distinction between long and short wavelengths is a natural one . For example, space-charge effects may be important for the high currents typically employed at long wavelengths, and the dominant interaction mechan ism is often coherent Raman scattering. In addition, dispersion due to the dielectric effects and finite transverse dimensions in the drift tubes and cavities are important at longer wavelengths. The principal goals at long w avelengths are to achieve much higher average powers with good overall effi ciency in a compact design. (C) 1999 Elsevier Science B.V. All rights reser ved.