Femto-second electron pulses from an rf linear accelerator as a far-infrared radiation source

Femto-second radiation pulses are becoming an important tool for studying the dynamics of materials at an atomic level. Various methods of generating femto-second electron pulses have been developed, including a thermionic rf gun combined with an alpha magnet. In this paper, we focus on the utilization of a photo-cathode rf gun and an rf linear accelerator to generate far-infrared (FIR) radiation. We demonstrate that with a magnetic chicane the electron beam pulse can be compressed to less than rms 20 fs at an energy between 30 and 50 MeV Geometrical wake fields due to the rf linear accelerator and the coherent synchrotron radiation effects in the magnetic chicane are included in the study. We suggest a possible improvement of the existing 80 MeV rf linear accelerator at the Pohang Accelerator Laboratory to employ it as a coherent FIR radiation source. We focus on extending the radiation wave number mu (= 1/lambda) to greater than 1500 cm(-1) with a micro-pulse energy of more than 100 mu J, which are the conditions required for femto-dynamics studies.