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Proceedings Paper

Optical Guiding And Beam Bending In Free-Electron Lasers
Author(s): E. T. Scharlemann
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Paper Abstract

The electron beam in a free-electron laser (FEL) can act as an optical fiber, guiding or bending the optical beam. The refractive and gain effects of the bunched electron beam can compensate for diffraction, making possible wigglers that are many Rayleigh ranges (i.e., characteristic diffraction lengths) long. The origin of optical guiding can be understood by examining gain and refractive guiding in a fiber with a complex index of refraction, providing a mathematical description applicable also to the FEL, with some extensions. In the exponential gain regime of the FEL, the electron equations of motion must be included, but a self-consistent description of exponential gain with diffraction fully included becomes possible. The origin of the effective index of refraction of an FEL is illustrated with a simple example of bunched, radiating dipoles. Some of the properties of the index of refraction are described. The limited experimental evidence for optical beam bending is summarized. The evidence does not yet provide conclusive proof of the existence of optical guiding, but supports the idea. Finally, the importance of refractive guiding for the performance of a high-gain tapered-wiggler FEL amplifier is illustrated with numerical simulations.

Paper Details

Date Published: 23 July 1988
PDF: 13 pages
Proc. SPIE 0738, Free Electron Lasers, (23 July 1988); doi: 10.1117/12.939690
Show Author Affiliations
E. T. Scharlemann, Lawrence Livermore National Laboratory (United States)


Published in SPIE Proceedings Vol. 0738:
Free Electron Lasers
Brian Emerson Newnam, Editor(s)

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