SOI-based micro-mechanical terahertz detector operating at room-temperature

We present a micro-mechanical terahertz (THz) detector fabricated on a silicon on insulator (SOI) substrate and operating at room-temperature. The device is based on a U-shaped cantilever of micrometric size, on top of which two aluminum half-wave dipole antennas are deposited. This produces an absorption extending over the $\sim 2-3.5$THz frequency range. Due to the different thermal expansion coefficients of silicon and aluminum, the absorbed radiation induces a deformation of the cantilever, which is read out optically using a $1.5\mu$m laser diode. By illuminating the detector with an amplitude modulated, 2.5 THz quantum cascade laser, we obtain, at room-temperature and atmospheric pressure, a responsivity of $\sim 1.5 \times 10^{8}$pm/W for the fundamental mechanical bending mode of the cantilever. This yields an noise-equivalent-power of 20 nW/Hz$^{1/2}$ at 2.5THz. Finally, the low mechanical quality factor of the mode grants a broad frequency response of approximately 150kHz bandwidth, with a response time of $\sim 2.5\mu$s

Observation of self-mode-locked pulses in terahertz quantum cascade lasers with real-time intracavity self-detection

Mode-locking operation and multimode instabilities in Terahertz (THz) quantum cascade lasers (QCLs) have been intensively investigated during the last decade. These studies have unveiled a rich phenomenology, owing to the unique properties of these lasers, in particular their ultrafast gain medium. Thanks to this, in QCLs a modulation of the intracavity field intensity gives rise to a strong modulation of the population inversion, directly affecting the laser current. In this work we show that this property can be used to monitor in real-time the temporal dynamics of multimode THz QCLs, using a self-detection technique combined with a broadband real-time oscilloscope. We study a 4.2THz QCL operating in free-running, and observe the formation of current pulses associated with trains of self-mode-locked optical pulses. Depending on the current pumping we find alternating regimes of unstable and stable pulse trains, respectively at the fundamental cavity repetition rate and its second harmonic. We interpret these measurements using a set of effective semiconductor Maxwell-Bloch equations that qualitatively reproduce the fundamental features of the laser dynamics, and also provide evidence in support of the solitonic nature of the observed pulses