The FELIX project1 involves the construction and operation of an infrared to millimeter-wave free electron laser facility. In the first phase of the project, an rf linac will supply electron pulses with energies adjustable between 15 and 45 MeV, a pulse length of 3 ps, peak current of 70 A, and repetition frequency of 1 GHz in 20-μs bursts. A permanent magnet undulator with thirty-eight periods of 65-mm length and variable strength (K = 0.55-1.9) will be used to cover the wavelength range from 8 to 80 μm. At wavelengths >25 μm, the slippage length exceeds the electron micropulse length, and short pulse effects are important. Computer simulations based on the self-consistent wave equation driven by single particle currents2,3 have been used to determine the pulse evolution and verify the results of analytic short pulse theories.4,5 Operation at 70 μm with sufficient gain to attain saturation within 8 μs and with a saturated micropulse peak output power of 10 MW appears feasible. Simulations also show that beam focusing effects increase the gain at long wavelengths. The coherence length of the laser pulses is limited by the duration of the electron pulses, and the laser will emit multimode broadband radiation. The pulse repetition time of the accelerator is short compared to the round trip time of an optical pulse in the resonator cavity, and so a large number of optical pulses is present in the cavity at any time. An intracavity interferometric element can be used to induce coherence between successive normally independent pulses.
© 1989 Optical Society of AmericaPDF Article