New schemes of THz generation by Free Electron devices

There are a number of schemes that have been investigated over the years to generate coherent radiation from free electrons in the mm-wave and Terahertz regions of the spectrum covering a wide frequency range from approximately 100 GHz to 10 THz. At such long wavelengths, good performance in terms of output power and gain can be achieved with a short length of the interaction region and with different mechanisms of energy transfer from the electron beam to the radiation field. These include the magnetic undulator originally proposed by Motz, which was employed by Phillips in the Ubitron back in 1960 and eventually led to the realization of the first free electron laser (FEL) in 1977, dielectric loaded waveguides for Cerenkov emission, and metal grating devices, based on the Smith-Purcell effect. The growing applications of THz radiation in a variety of different fields are demanding versatile sources that combine compactness and challenging performance. In this paper we will present novel schemes for exploring the limits in performance of radio-frequency driven free electron devices in terms of ultra-short pulse duration, wide bandwidth operation and energy recovery for near CW operation.