Microplasma Traveling Wave Terahertz Amplifier

We describe a traveling wave terahertz (0.75-1.1 THz) amplifier that uses a meandering TE₀₁ waveguide coupled to a plasma beam and discuss its design, microfabrication, and cold/hot tests. Motivations for using plasmas instead of electron beams are: 1) thermionic emission required in e-beam generation can be replaced with gas ionization, 2) electrostatic lenses and magnetic focusing structures can be eliminated or reduced in complexity since plasmas can be self-focusing, 3) larger acceleration fields can be used by taking advantage of plasmas' space-charge electric fields of ~10⁴-10⁶ V/cm, 4) the plasma pressure can be lowered to yield an electron beam in the limit when the devices' critical dimensions are smaller than the electron mean-free path, and, hence, 5) higher power amplifications at higher efficiency can be achieved. Cold tests showed that a dielectric coating (50-nm Al₂O₃) of the gold-coated meandering silicon waveguide improved the maximum terahertz transmission (S₂₁) from -20 to -15 dB. Hot tests showed 12-dB gain at a center frequency of ~0.9 THz over a 1-GHz bandwidth.