A tunable coherent IR radiation source based on a self-amplified spontaneous emission free-electron laser

A coherent tunable infrared (IR) radiation source of 5-80 μm wavelengths based on a self-amplified spontaneous-emission (SASE) free-electron laser (FEL) is presented. It is numerically demonstrated that the output electromagnetic radiation becomes fully coherent both transversely and longitudinally with variable wavelengths by changing the electron-beam energy or varying the undulator gap. The self-amplified spontaneous emission of the radiation is achievable in relatively short saturation length with approximately 300 fs or longer pulse length of the electron beam which can be easily produced by a photocathode rf gun. The computer programs, PARMELA and GENESIS, are utilized to investigate the electron beam characteristics in the linear accelerator and the influence of beam parameters on the performance of the FEL, respectively. The spectral tunability of the optimized undulator shows the saturated power and saturation length. The parameters of the IR FEL are easily realizable with a conventional rf linear accelerator and permanent undulator magnet.