LONG-WAVELENGTH FREE-ELECTRON LASERS IN 1995

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 las ers is presented. The distinction between long and short wavelengths i s a natural one since different physical processes may be important. S pace-charge effects may be important for the high currents typically e mployed at long wavelengths, and the dominant interaction mechanism is often coherent Raman scattering. In addition, dispersion due to the d ielectric effects and finite transverse dimensions in the drift tubes and cavities are important at longer wavelengths. The principal goals at long wavelengths are to achieve much higher average powers with goo d overall efficiency in a compact design, and the highest average powe r produced in an FEL to date (36 W) has been recorded in the Ku-band.