Wave profile modification (optical guiding) induced by free-electron laser interaction.

Abstract

Modification of the transverse intensity profile of a single electromagnetic waveguide mode during the free-electron laser (FEL) interaction has been measured. This effect is the waveguide analog to free-space optical guiding. The studies were carried out at microwave frequencies (8--12 GHz) in a FEL with use of a mildly relativistic electron beam of \ensuremath{\simeq}200 kV energy and \ensuremath{\simeq}1.0 A current. The probing of the rf fields was accomplished by small electric dipole antennas inserted in the interaction region. The observed intensity profiles are compared with the measured FEL-induced phase shifts (wave refractive index).