  A scheme of THz radiation using two moderately intense lasers and a
moderately relativistic electron beam is proposed. In the scheme, a laser
encounters a co-propagating relativistic electron beam, and excites plasmons
via the two-plasmon decay. The excited plasmons will emit the THz radiations,
interacting with the second laser via the Raman scattering. Our estimation
suggests that the mena-free-path of the pump laser to the THz radiation is much
shorter than the Thomson scattering. The physical parametes for practical
interests are presented.
