Free electron lasers using 'beam by design'

Several methods have been proposed in the literature to improve free electron laser output by transforming the electron phase-space before entering the FEL interaction region. By utilizing 'beam by design' with novel undulators and other beam changing elements, the operating capability of FELs may be further usefully extended. This paper introduces two new such methods to improve output from electron pulses with large energy spreads and the results of simulations of these methods in the 1D limit are presented. Both methods predict orders of magnitude improvements to output radiation powers. (paper)