Imaging in the frequency range between 100 GHz and 1 THz using Compact Free Electron Lasers, Doria, A., Gallerano G.P., Germini M., Giovenale E., Lai A., Messina G., Spassovsky I., and d'Aquino Luigi , IRMMW-THz 2006 - 31st International Conference on Infrared and Millimeter Waves and 14th International Conference on Terahertz Electronics, Shanghai, p.161, (2006)