AMPLIFICATION OF MONOCHROMATIC SHORT-WAVELENGTH RADIATION DURING THE STOCHASTIC DECELERATION OF A RELATIVISTIC ELECTRON STREAM IN AN INCOHERENT PUMP FIELD

The use of incoherent multiwave pump radiation or randomly varying mag netostatic fields (stochastic undulators) for improving the energy con version efficiency in free-electron lasers based on stimulated wave sc attering and the stimulated undulator emission of relativistic electro n beams is proposed. It is shown within the quasilinear approximation that the electronic efficiency increases in proportion to the width of the pump spectrum due to enrichment of the spectrum of combination wa ves which are synchronous with the electron beam and realization of a mechanism of stochastic particle deceleration when the signal wave is monochromatic. At the same time, the efficiency scarcely depends on th e spread of the beam parameters, making the use of the method promisin g for improving the efficiency of free-electron lasers powered by inte nse relativistic electron beams. (C) 1997 American Institute of Physic s. [S1063-7842(97)01407-4].