  The collective and single-electron amplification regimes of a non-collinear
free electron laser are analyzed within the framework of dispersion equations.
The small-signal gain and the conditions for self-amplified excitations are
found. The collective excitations in a free electron laser are shown to be
favored by the non-collinear arrangement of the relativistic electrons and the
laser wave. Implications for free-electron lasing without inversion are
discussed.
