Technology development for tapered-wiggler free-electron lasers

This report addresses technology required for high-power visible free-electron lasers. The work follows logically from recent demonstrations of electron kinetic energy conversion to optical energy in tapered-wiggler free-electron lasers (FEL). The tapered-wiggler FEL differs from the first demonstrated nontapered version in that it allows a much larger fraction of electron energy to be converted to optical energy in a single pass through the wiggler magnet. This conversion, now demonstrated as high as 4 percent, may lead to high-power, high-efficiency devices if an e-beam recovery stage is added downstream of the wiggler. The technology addressed is that necessary for the transition from the current 10 micron amplifiers to 0.5 micron oscillators. These two regimes differ dramatically in two ways. First, the physics of the oscillator is more complex than for the existing low-gain amplifiers because the optical wave in the oscillator is not predetermined by an injector. Second, a higher level of electron and photon beam control is required to get proper physical overlap of these beams at shorter wavelengths.