  We propose a terahertz radiation source based on the excitation of plasma
resonances in graphene structures by means of mixing two NIR laser signals with
a THz difference frequency. The process is the photo-thermo-electric effect
which has recently been demonstrated to be operative at THz frequencies in
graphene. An antenna couples the THz radiation out of the sub-wavelength
graphene element and into the far field. The emission is monochromatic with a
bandwidth determined by that of the NIR laser sources. The output power of the
device as a function of the emitter frequency is estimated at tens of
microWatts.
