Common mode frequency instability in internally phase-locked terahertz quantum cascade lasers.

Feedback from a diode mixer integrated into a 2.8 THz quantum cascade laser (QCL) was used to phase lock the difference frequencies (DFs) among the Fabry-Perot (F-P) longitudinal modes of a QCL. Approximately 40% of the DF power was phase locked, consistent with feedback loop bandwidth of 10 kHz and phase noise bandwidth ~0.5 MHz. While the locked DF signal has ≤ 1 Hz linewidth and negligible drift over ~30 min, mixing measurements between two QCLs and between a QCL and molecular gas laser show that the common mode frequency stability is no better than a free-running QCL.

A plasmonic terahertz detector with a monolithic hot electron bolometer.

A plasmonic terahertz detector that integrates a voltage-controlled planar barrier into a grating gated GaAs/AlGaAs high electron mobility transistor has been fabricated and experimentally characterized. The plasmonic response at fixed grating gate voltage has a full width at half-maximum of 40 GHz at ∼405 GHz. Substantially increased responsivity is achieved by introducing an independently biased narrow gate that produces a lateral potential barrier electrically in series with the resonant grating gated region. DC electrical characterization in conjunction with bias-dependent terahertz responsivity and time constant measurements indicate that a hot electron bolometric effect is the dominant response mechanism at 20 K.