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High-Gain High-Efficiency FELs

High energy and high-power lasers have found wide usage in research and application including material processing, solid-state research, particle physics, and as drivers for other radiation sources such as x-ray (K-alpha) production. From early proposals of laser driven accelerators to recent applications such as high-field physics, nuclear physics, fusion science, proton-beam generation, and radiography, the demand for high power and high-energy lasers has increased.

Lasers in the greater than 100 TW or 10 J class are challenging to build, involve large investments, and can only be developed for a limited set of wavelengths. While thermal limits and optical-damage thresholds constraint the selection of gain media, the lack of viable pump-sources further restricts usable materials. Flashlamps produce large thermal-loads and are not suited to materials with short fluorescence-times (such as Ti:S). Diodes remain expensive, difficult to use on very large crystals, and are more practical at longer wavelengths.

Free-electron lasers (FELs) have long promised to provide high average optical-powers, and recent work indicates that this promise can be delivered upon by increasing the efficiency, duty factor and bunch repetition-rate of existing designs. The achievement of very high average power free-electron laser performance has bee typically been pursued by use of oscillator configurations, with beams of quality less than state-of-the-art.

PBPL's approach is to use a high-efficiency single-pass high-gain FEL to achieve high peak and average powers. A high-brightness photoinjector coupled with either a magnetic compressor or a velocity bunching scheme is used to produce beams of moderate energy (~100MeV) but very high peak current (~kA). This dense beam is sent into an undulator with a tapered section to extract ~10% or more of the electron beam energy as radiation.

Of the many applications possible for a high-average power FEL, we consider two novel ones in this section: