We report the control of an emission direction in two-dimensional (2D) angular space for the terahertz master-oscillator power-amplifier quantum cascade lasers. The device exploits a rhombohedral array of subwavelength air slits as the wave coupler. The available range of the emission direction and the polarization state are determined by the unit slit, while the emission direction and the beam divergence are determined by the array configuration. An analytic relationship between the beam direction and the array parameters was established and experimentally confirmed. The lasers exhibit single mode emission around 3.4 THz, with a low divergence of 14° × 14°. The resultant emission direction varies controllably in a range that the polar angle belongs to 0° to 70° and the azimuth angle belongs to 0° to 90°, which can be further extended.

We report on the continuous-wave (CW) operation of 1D terahertz quantum cascade (THz QC) microlaser arrays working on various bound states in the continuum (BICs). We first created a quasi-BIC state by breaking the inversion symmetry of the microlaser array, which enables flexible control of the radiation efficiency. The optimized multi-periods array exhibits single-mode emission with the maximum output power of 21 mW (at 30 K), and the maximum operation temperature (Tcw) of 45 K. To further increase Tcw, we created a hybrid-BIC state by hybridizing a quasi-BIC generated in a few-periods array and a high-Q surface plasmon polariton mode formed in an unbiased array. The hybridization minimizes the pumping area with no obvious degradation of the threshold current density. The reduced pumping area, together with the discrete distribution of microlasers, significantly decreases the device thermal resistance. Such scheme improves the Tcw up to 79 K with a low beam divergence of 17°×17°, and the output power remains 3.4 mW at 20 K. Our work provides a novel solution to control the output power, the operating temperature, and the beam quality of THz QC lasers in CW mode.

The development of high performance is essential for the realization of ultra-broadband imaging technology, which can be widely used in astronomy, medical health, defense and security, and many other applications. In this work, we demonstrate an ultra-broadband upconversion device based on a heterojunction interfacial work function internal photoemission (HEIWIP) detector and an AlGaAs/GaAs/In0.04Ga0.96 As quantum well LED. The up-converter exhibits an ultra-broad response covering from the terahertz to mid-infrared region (3–165 THz) due to free carrier absorption and inter-valence-band absorption in p-type based photodetectors. The peak responsivity in the terahertz and mid-infrared region is measured to be 7.2 A/W at 9.2 THz and 3.5 A/W at 28.8 THz, respectively, which is improved by an order of magnitude compared to the previous homojunction interfacial work function internal photoemission-based up-converter (0.5 A/W) in the THz region. The up-converter also demonstrates an improved upconversion efficiency of 1.5%. The noise equivalent power (NEP) of the imaging system consisting of the HEIWIP-LED up-converter and Si CCD is studied. The optimized NEP can achieve ∼10 pW/Hz1/2 in both terahertz and mid-infrared regions. The HEIWIP-LED up-converter exhibits excellent properties of high responsivity, ultra-broad response, and low noise, making it a great prospect for future applications in the field of ultra-broadband imaging.