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    Lasing with a Near-Confocal cavity in a high power FEL

    Lasing at high power in FELs has been achieved so far only with a near-concentric resonator [1]. Though this design can scale up to quite high power, it is ultimately limited by the mirror steering stability as the resonator design approaches concentricity. This constraint may be avoided by using a near-confocal resonator operated in a ring configuration. It is found that, if a small amount of gain focusing is present, the near-confocal resonator eigenmodes are modified such that the lowest order mode collapses around the electron beam and is large in the return (non-focusing) direction. This eigenmode is stable and is relatively insensitive to changes in the mirror radii of curvature and the strength of the electron beam focusing. This paper will present the theory of this new concept. This work supported DOE Contract DE-AC05-84ER40150, the Office of Naval Research, the Commonwealth of Virginia, and the Laser Processing Consortium.

    Lase 2002, Photonics West, 19-25 January 2002, San Jose, CA, to be published in SPIE proceedings volume 4632

    Author(s): Stephen Benson, George Neil, Michelle Shinn



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