Raman and Thompson regimes of amplification in a wiggler with noncollinear laser and electron beams

The collective and single-electron amplification regimes of a noncollinear free-electron laser (FEL) are studied within the framework of dispersion equations. In the limit of small-signal gain the growth rates and the conditions for self-amplified excitations are found for the collective (Raman) and single-electron (Thompson) regimes. The Raman regime is shown to be preferable for the coherent spontaneous second harmonic generation by ultrarelativistic electron beams. Raman excitations in a noncollinear FEL, e.g., in an FEL without inversion, are favored by the noncollinear geometry of the electron and the laser beams, and by the relativity of the beam electrons.

Figure 1

The growth rate as a function of beam current.

Figure 2

The dependance of $\delta$ from beam current.

Figure 3

The evolution of fields amplitudes for Raman regime, when $\mid q\mid =0.051$. The vertical lines denote the moments of time, for which beam phase planes are presented in Fig. 4.

Figure 4

The phase planes of the beam in different moment of time for Raman type: $\mid q\mid =0.051$.

Figure 5

The evolution of fields amplitudes for Thompson regime, when $\mid q\mid =6.42$. The vertical lines denote the moments of time, for which beam phase planes are presented in Fig. 6.

Figure 6

The phase planes of the beam in a different moment of time for Thompson type: $\mid q\mid =6.42$.