Free Electron Laser Equations Research Articles

Optical guiding in a free electron laser

The coherent interaction between an optical wave and an electron beam in a free electron laser (FEL) is shown to be capable of optically guiding the light. The effect is analyzed using a two-dimensional approximation for the FEL equations, and using the properties of optical fibers. Results of two-dimensional (cylindrically symmetric) numerical simulations are presented, and found to agree reasonably well with the analytically derived criterion for guiding. Under proper conditions, the effect can be large and has important applications to short wavelength FELs and to directing intense light.

Formulation of normalized nonlinear free electron laser equations

The general nonlinear self-consistent equations describing the FEL in the steady-state amplifying configuration is derived with the space-charge effects and all the efficiency enhancement schemes: (i) a spatially varying wiggler amplitude and/or period and (ii) a dc electric field Edc (z) = [−∂φdc /∂z]êz. All the efficiency enhancement schemes are shown to be somewhat equivalent. For a variable period magnetic wiggler, the FEL equations can be appropriately normalized to a three-parameter set of coupled equations. All operating regimes are covered by these normalized equations. The condition for space charge to be unimportant is given. In the absence of the space-charge effects, the three-parameter set of equations reduces to a two-parameter set. The inclusion of additional efficiency enhancement schemes increases the number of parameters to describe the FEL. Curves showing the efficiency, radiation amplitude, and growth rate will be presented.

Nonlinear Formulation and Efficiency Enhancement of Free-Electron Lasers

We present a general, self-consistent, nonlinear theory of the free-electron laser (FEL) process. The formulation of the temporal steady-state problem results in a set of coupled nonlinear FEL equations governing the spatial evolution of the amplitudes and wavelengths of the fields. We show that intrinsic FEL efficiencies can be greatly enhanced by spatially contouring the magnetic pump-field parameters. In the optical regime, the single-pass efficiencies are found to exceed 20%.