Generation of intense uv radiation by subharmonically seeded single-pass free-electron lasers

We present a detailed analysis of a subharmonically seeded single-pass free-electron laser (FEL) utilizing two wiggler magnets separated by a dispersion section. To be specific, suppose the seed to be laser light at 300 nm. A first wiggler is used to energy modulate the electron beam. This is followed by a dispersion section to produce spatial bunching, and a second wiggler resonant to 100 nm. Upon passing through the second wiggler, the prebunched electron beam first radiates coherently, and then this radiation is exponentially amplified. Finally, a tapered section is used to extract additional power from the electron beam. In this manner we can achieve pulses of duration ≊10 psec with 1 mJ per pulse in 10^-4 bandwidth, with continuously tunable wavelength in the range 100–300 nm. We present the analytical tools we have employed for the preliminary estimate of the system performance and of the optimization of the parameters. We describe our modification of the simulation code tda to include harmonic generation and discuss its use in analyzing the subharmonically seeded FEL. The analytic and computer-simulation calculations are in good agreement. We discuss in detail the physical process in the system and the optimization of parameters.