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We have combined few-cycle THz spectroscopy with quantum cascade technology. This combination allows to perform unique THz time-domain measurements of THz-QCLs. By coupling the few-cycle THz pulse into the waveguide of the QCL, the processes within the active zone can be probed. This gives direct information regarding the energy, dynamics and coherence of transitions in the QCL structure. In addition,...
THz quantum cascade (QC) lasers with an active-region thickness of 5.86 mum was demonstrated. The current threshold was then reduced by reducing the device surface. The laser resonator is based on a micro-cylindrical geometry. In general micro-cylindrical resonators rely on total-internal reflection on the cavity sidewalls in order to confine the light. The small (r=25 mum) and medium (r=37.5 mum)...
We demonstrate terahertz microcavity lasers at lambda=112 mum with ultra-low current thresholds of 4 mA and with mode volumes of less than one-cubic-wavelength. Confinement in the longitudinal direction is obtained using almost-circular micro-disk resonators. The guiding properties of surface-plasmons are exploited to guide the mode with the metal contact. The devices laser up to 70 K in pulsed mode,...
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