Anomalous (stimulated) Refraction Induced By Free-electron Laser Interaction

The stimulated refraction effect (optical guiding) in a free-electron laser (FEL) is studied theoretically. The analysis of the 3-dimensional FEL wave equation is performed according to two different thermal methods. First, the microwave field is expanded into vacuum waveguide modes, in which case the optical guiding appears as an active mode-coupling effect. In the second method, the eigenmodes of the FEL radiation field are found, which yields both the gain of the system (complex eigenvalues) and the radial intensity distribution of the interacting waves, describing the guiding effect. Computer calculations show that optical guiding may have a strong influence on both the gain and mode content of millimeter-wave FELs.