Compton Mode Conversion of Laser Beat Wave-Driven Plasma Wave by an Electron Beam in a Plasma Channel

A large amplitude plasma wave, driven by beating two lasers in a depressed density plasma channel, is shown to effectively couple to a mildly relativistic electron beam to produce terahertz (THz) radiation. The plasma wave parametrically couples the THz electromagnetic mode to a negative energy beam space charge mode, and both decay waves grow at the expense of the beam and the plasma wave. In the low beam current Compton regime, the growth rate scales to one-third power of beam current and two-thirds power of plasma wave amplitude.