Stable-unstable resonator design for a wide-tuning-range free-electron laser

A stable-unstable resonator design which employs a one-sided negative-branch unstable mode in the plane perpendicular to the wiggler magnetic field and a stable Gaussian cavity mode in the perpendicular direction can provide a near-ideal solution for a very-wide-tuning-range infrared free-electron laser. A trial design which provides for all-reflective optics, reasonable output coupling, and potentially continuous tunability from 3 to 50 mu m in a single resonator is described.<
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