Workpackage 1.
1. We demonstrate quasi-crystal distributed feedback lasers with 240 mW peak optical power, and the highest slope efficiency (570 mW/A at 78K, 700 mW/A at 20K) reported to date in an electrically pumped multimode, surface emitting, disordered THz laser.
2. We demonstrated the first THz random lasers operating in continuous-wave
3. We develop high power, single mode, low divergence THz wire lasers.
4. we demonstrate requency modulated THz combs showing a proliferation of emitted modes over the entire gain bandwidth and across more than 60% of its operational range, with ≈0.18 mW per mode optical power.
Workpackage 2.
- Task 2.1 and Task 2.3 : We fabricated THz saturable absorbers by transfer coating and inkjet printing single and few-layer graphene films prepared by liquid phase exfoliation of graphite, demonstrating transparency modulation ∼80%, almost one order of magnitude larger than that reported to date at THz frequencies.
- Task 2.2: we demonstrate THz saturable absorption in multilayer graphene films, grown via CVD on Nickel.
- Task 2.4: We engineer miniaturized THz FCSs, comprising a heterogeneous THz QCL, integrated with a tightly coupled, on-chip, solution-processed, graphene saturable-absorber reflector that preserves phase-coherence between lasing modes, even when four-wave mixing no longer provides dispersion compensation. This enables a high-power (8 mW) FC with over 90 optical modes, through 55% of the laser operational range.
- Task 2.4: We demonstrate mode-locking in surface-emitting electrically-pumped THz random QCLs.
- Task 2.5: We develop electrically switchable graphene THz modulators with a tunable‐by‐design optical bandwidth. Electrostatic gating is achieved by a metal grating used as a gate electrode, with an HfO2/AlOx top gate dielectric. This is patterned on a polyimide layer, which acts as a quarter wave resonance cavity, coupled with an Au reflector underneath.
- Task 2.6: we demonstrate THz saturable absorber mirrors based on intersubband-polaritons.
Workpackage 3.
- Task 3.1: we demonstrate uncooled THz photodetectors (PDs) showing high sensitivity (NEP ≤ 160 pW Hz–1/2), fast response time (hundreds ps response time), and a 4 orders of magnitude dynamic range is achieved making our devices the fastest, broad-band, low-noise, room-temperature THz PD, to date.
- Task 3.1: We develop THz detectors based on antenna-coupled field-effect transistor (FET) with an active channel of Se-doped black phosphorus. Room-temperature responsivity of 3 V W−1 is achieved , with NEPs of 7 nW Hz−1/2 at 3.4 THz.
- Task 3.2: we develop highly efficient nanowire THz detectors and by coupling a THz QCL to scattering-type scanning near-field optical microscopy (s-SNOM) and monitoring both electrical and optical readouts, we simultaneously measure transport and scattering properties. The spatially resolved electric response provides unambiguous signatures of photo-thermoelectric and bolometric currents in the nanowire.
- Task 3.3: we demonstrate a self-starting miniaturized ultra-short pulse THz laser, exploiting an original device architecture that includes the surface patterning of multilayer-graphene saturable absorbers distributed along the entire cavity of a double-metal semiconductor 2.30–3.55 THz wire laser. Self-starting pulsed emission with 4.0-ps-long pulses in a compact, all-electronic, all-passive and inexpensive configuration is demonstrated.
- we demonstrate mode-locking in surface-emitting electrically pumped random THz QCL, major goal of SPRINT
Workpackage 4.
- Metrology: By exploiting a metrological grade system comprising a THz frequency comb synthesizer, we measure, for the first time, the free-running emission linewidth the tuning characteristics, and the absolute center frequency of individual emission lines of different frequency generation THz QCLs with an uncertainty of 4 × 10−10.
we demonstrated full stabilization and control of the two key parameters - carrier offset frequency and frequency separation between optical modes - of a THz QCL-comb against the primary frequency standard.
- Spectroscopy: We develop a bow-tie resonant cavity for THz radiation, injected with a continuous-wave 2.55 THz QCL. The bow-tie cavity employs a wire-grid polarizer as input/output coupler and a pair of copper spherical mirrors coated with an unprotected 500 nm thick gold layer. The improvements with respect to previous setups have led to a measured finesse value F = 123, and a quality factor Q = 5.1105.
- Microscopy: we devised a THz s-SNOM system that provides both amplitude and phase contrast, and achieves nanoscale (60-70nm) in-plane spatial resolution. It features a QCL that simultaneously emits THz frequency light and senses the backscattered optical field through a voltage modulation induced inherently through the self-mixing technique and employed it to test THz polaritons in topological insulators.
- Ultrafast photonics: we designed a SiO2/black phosphorus/SiO2 heterostructure in which the surface phonon modes of the SiO2 layers hybridize with surface plasmon modes in black phosphorus that can be activated by photo-induced interband excitation within ∼50 fs and disappears within 5 ps, as the electron–hole pairs in black phosphorus recombine.
