Dynamical frequency pulling of degenerated and nondegenerated modes in small mode volume whispering-gallery terahertz quantum-cascade lasers

We present terahertz quantum-cascade lasers based on sub-wavelength circular-shaped double-metal microcavities whose single-mode emission can be fine-tuned via dynamical frequency pulling. This allows to estimate the peak gain of the material to View the MathML source and the shift of the cavity mode towards the gain maximum by 30 GHz. Strong mode confinement in the growth and in-plane directions are provided by a double-plasmon waveguide and due to the strong impedance mismatch between the gain material and air. These ultra-compact devices exhibit threshold currents as low as 13.5 mA. We lifted the natural two-fold degeneracy of the whispering-gallery modes by lifting the rotational symmetry of such resonators.