Abstract

Conventional free electron lasers (FELs) suffer from some drawbacks related to the large size of most electron beam (ebeam) accelerators that implies high costs, system complexity, and shielding requirements. However, in the far infrared (FIR) and millimetre (mm) wave region the FEL can meet the demand of compactness. For example, the low ebeam energies required (<10 MeV) allow the use of small size accelerators like radio-frequency (rf) linacs or microtrons. The increased performance in terms of gain at wavelengths in the FIR and mm also requires a shorter length of the interaction region, thus allowing the use of short period undulators and a small number of periods which results in a better efficiency. Moreover, the presence of a dispersive element inside the undulator, like a waveguide needed for operation at long wavelengths, alters the radiation generation mechanism introducing new tuning possibilities in addition to those traditional for the FELs. The performance of such a device shows very peculiar characteristics like the possibility of changing the central frequency and the spectral bandwidth for spectroscopical purposes or the high peak power for applications in nonlinear optics. Following the above considerations the FEL group at the ENEA Frascati Research Centre has started a development program for compact FEL devices. A first prototype is now running, since 1992, in the mm wave region, and a second development step to move toward the FIR region is in progress.

© 1994 IEEE