Short Rayleigh length free electron lasers
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Authors
Colson, W.B.
Blau, J.
Armstead, R.L.
Crooker, P.P.
Vigil, R.
Voughs, T.
Williams, B.W.
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Advisors
Date of Issue
2006
Date
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Abstract
Conventional free electron laser (FEL) oscillators minimize the optical mode volume around the
electron beam in the undulator by making the resonator Rayleigh length about one third to one half of the
undulator length. This maximizes gain and beam-mode coupling. In compact configurations of highpower
infrared FELs or moderate power UV FELs, the resulting optical intensity can damage the
resonator mirrors. To increase the spot size and thereby reduce the optical intensity at the mirrors below
the damage threshold, a shorter Rayleigh length can be used, but the FEL interaction is significantly
altered. We model this interaction using a coordinate system that expands with the rapidly diffracting
optical mode from the ends of the undulator to the mirrors. Simulations show that the interaction of the
strongly focused optical mode with a narrow electron beam inside the undulator distorts the optical wave
front so it is no longer in the fundamental Gaussian mode. The simulations are used to study how mode
distortion affects the single-pass gain in weak fields, and the steady-state extraction in strong fields.
Type
Article
Description
The article of record as published may be located at http://dx.doi.org/10.1103/PhysRevSTAB.9.030703
Series/Report No
Department
Physics
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Funder
The authors are grateful for the support from NAVSEA, ONR, and the JTO.
Format
Citation
Physical Review Special Topics, Accelerators and Beams, Volume 9, 030703 (2006)
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.