Terahertz quantum cascade laser implementing a {hacek over (C)}erenkov difference-frequency generation scheme

A terahertz quantum cascade laser comprising:

• a substrate, wherein an exit facet of said substrate is polished at an angle between 10° to 40°;
• a doped current extraction semiconductor layer positioned on said substrate;
• an active region layer positioned above said current extraction semiconductor layer, wherein said active region layer is arranged as a multiple quantum well structure, wherein said current extraction semiconductor layer is used for lateral current extraction from said active region layer;
• a metallic contact electrically connected to said current extraction semiconductor layer for current extraction from said active region layer;
• a first one or more waveguide cladding layers between said current extraction semiconductor layer and said action region layer;
• a second one or more waveguide cladding layer in contact with and above said active region layer, wherein said first and second one or more waveguide cladding layers are disposed to form a waveguide structure to guide mid-infrared light;
• and
• metal contact layers in contact with said second one or more waveguide cladding layers;
• wherein a propagation constant of a nonlinear polarization wave (knl), given by a difference between propagation constants of mid-infrared pumps in said waveguide structure, in said active region layer is smaller compared to a propagation constant of a terahertz radiation (kTHz) propagating in said substrate, wherein said terahertz radiation is emitted into said substrate at a {hacek over (C)}erenkov angle relative to a direction of said nonlinear polarization wave, wherein said terahertz radiation once in said substrate propagates towards said exit facet.