Conference Agenda

We have demonstrated experimentally how ultrabroadband inverse spin Hall emitters present an unprecedented new scheme for room temperature THz frequency comb generation. Building on previous proof-of-principle demonstrations, we demonstrate here by improved experimental developments how this spintronics comb downconversion effectively does not present any frequency rolloff at least up to 1,05THz, contrary to standard photoswitches. A theoretical and numerical model implementing spin Hall dynamics in nanometric FM/HM stacks predict photomixing bandwidths up to 10THz.

Van der Waals heterostructures offer engineered materials with physical phenomena, including optical nonlinearities and spin-to-charge conversion. However, their use in the terahertz range has been limited due to reliance on exfoliated materials, restricting scalability. Here, we realize large-area crystalline heterostructures combining topological insulators, TMDs, and ferromagnets, enabling terahertz electronic and spin currents via optical down-conversion.

We demonstrate how TMD polymorphs (1T′, 2H, 3R) significantly alter terahertz responses with a single monolayer change, influencing both electrical and magnetic properties. Additionally, crystal symmetry impacts magnetic behavior, revealing nonlinear effects in the 1T′ polymorph. This integration of diverse materials establishes a scalable platform for next-generation photonic, electronic, and spintronic devices.

Frequency mixing in the terahertz (THz) range holds promise for bridging the sub-THz and multi-THz spectral domains, critical for next-generation wireless communication and ultrafast signal processing [1]. We demonstrate room-temperature upconversion of broadband sub-THz signals (0.1–0.5 THz) into higher THz bands using a 70 nm-thick HgTe-based Dirac semimetal, leveraging its strong third-order nonlinear response without requiring resonant enhancement. The process relies on four-wave mixing (FWM), driven by the high χ(3) of HgTe, which arises from its gapless Dirac-like dispersion and long carrier relaxation times [2]. Our dual-source excitation scheme combines broadband pulses from a photoconductive antenna (PCA) with narrowband superradiant pulses from the TELBE source [3]. When coherently overlapped in the HgTe film, the input fields generate distinct frequency sidebands at f_high = f_T + f_a ​ and f_low = f_T - f_a, as expected for third-order FWM. A field conversion efficiency exceeding 2% was achieved—among the highest reported for solid-state THz nonlinear processes at ambient conditions [2]. The efficiency scaling with field strengths and polarization confirms the coherent and χ⁽³⁾-driven nature of the process. These results establish HgTe Dirac semimetals as highly promising platforms for THz photonics, with further enhancement anticipated from multilayer or metamaterial integration [4].

We present a simple and cost-effective single-arm technique for generating broadband circularly polarized THz radiation, achieving record ellipticity up to 0.99. By adjusting the chirp of the fundamental wave, the orientation, tilt, and position of a single BBO crystal, we obtain stable circular polarization up to 40 THz, with high ellipticity maintained to 8 THz. Notably, the polarization remains robust under chirp-induced spectral tuning, enabling bandwidth control without loss of polarization. Leveraging the high sensitivity of THz polarization to crystal alignment, we propose two high-speed modulators: a Pockels cell for nanosecond-scale control via FHW polarization rotation, and an acousto-optic beam deflector to modulate the pump incidence angle. These approaches enable real-time manipulation of THz polarization and emission direction, opening new possibilities in ultrafast communication, adaptive imaging, and polarization-sensitive spectroscopy.