LONG-WAVELENGTH FREE-ELECTRON LASERS IN 1997

A summary of the current status and most important future directions f or long wavelength ( greater than or equal to 0.5 mm) free-electron la sers are presented. The distinction between long and short wavelength is a natural one. For example, space-charge effects may be important f or the high currents typically employed at long wavelengths, and the d ominant interaction mechanism is often coherent Raman scattering. In a ddition, dispersion due to the dielectric effects and finite transvers e dimensions in the drift tubes and cavities are important at longer w avelengths. The principal goals at long wavelengths are to achieve muc h higher average powers with good overall efficiency in a compact desi gn, and the highest average power produced in a FEL to date (36W) has been recorded in the Ku-band. (C) 1998 Elsevier Science B.V. All right s reserved.