An improved longwave infrared quantum cascade laser. The improvement includes a strained InxGa1-xAs/AlyIn1-yAs composition, with x and y each between 0.53 and 1, an active region emitting at a wavelength equal to or greater than 8 μm, an energy spacing E54 equal to or greater than 50 meV, an energy spacing EC4 equal to or greater than 250 meV, and an optical waveguide with a cladding layer on each side of the active region. Each cladding layer has a doping level of about 2·1016 cm−3. The optical waveguide also has a top InP layer with a doping level of about 5·1016 cm−3 and a bottom InP layer with a doping level of about 5 1016 cm−3. Additionally, the optical waveguide has a plasmon layer with a doping level of about 8·1018 cm−3.