Small optical volume terahertz emitting microdisk quantum cascade lasers

The authors fabricate and characterize a series of quantum cascade laser micropillars emitting at approximate to 3.5 THz. The optical confinement by double plasmon guiding in the vertical direction creates a large impedance mismatch between the confined optical modes and free space. Thus, unlike standard dielectric structures, large quality (Q) factors are maintained for small radius to wavelength ratios. The narrow bandwidth of the optical mode results in low threshold current (8 mA) single-mode lasers. Cavity pulling enables a fine dynamic tuning of the emission wavelength. Comparison of the frequency shift due to cavity pulling and the Stark effect provides an experimental measure of the gain (36 cm(-1)).