s-Nebula develops terahertz technologies based on magnetic materials and spintronic phenomena that can have an impact on high frequency communications, non-destructive testing and ellipsometry. The project gathers expertise from France, Germany, Sweden and Czech Republic to face challenges in materials growth, terahertz spectroscopy, device modelling and evaluation as well as technological integration for industrialisation.
The TeraHertz (THz) frequency band represents a spectral window that offers rich opportunities for advanced applications in many fields, e.g. industrial quality control, spectroscopy, imaging, medical diagnostics, security, telecommunication and high-speed electronics. However, the development of THz technology is currently hampered by the limitations of available technological paradigms and there is an urgent need for a radically new THz technological framework. Recently, starting with pioneering work of consortium members, optically-driven spin based THz (s-THz) emitters were demonstrated, based on optically triggered spin currents and spin-to-charge conversion. A typical s-THz emitter is a nanometer-thick metallic heterostructure consisting of ferromagnetic (FM) and strongly spin-orbit-coupled nonmagnetic (NM) materials (see Fig 1). Pumping the s-THz emitter by a fs laser pulse leads to ultrafast demagnetization, followed by the emission of spin-current pulse converted by the inverse spin-Hall effect into an electric-dipole type emission of a broadband THz pulse (> 20 THz) into the optical far field. This s-THz emission possesses an efficiency matching state-of-the-art THz standards. In s-Nebula, we combined developments in the fields of spintronic with the expertise from THz technologist to address the full THz chain. The s-Nebula approach thus relies in both exploring new materials and new device geometries to enhance s-THz emission efficiency, together with developing new s-THz functionalities.
The achieved overall objectives are thus:
- The development of pulsed broadband (> 20 THz) with output power larger than conventional photoconductive switches, and the demonstration of tunable low power CW s-THz emitters with no-roll off above 1 THz.:
- The development of unified models describing spin transport, THz generation and propagation in complex structures,
- The demonstrate a fully operative spin-based THz detection mechanisms based on either Zeemand torque or spin-accumulation for pulsed regimes, and of proof of concepts of CW detectors using antiferromagnetic materials.
- The development of s-THz devices with modulation rate as large as 10 MHz and with a full polarization control (extinction ratior > 25 dB).
The s-NEBULA project also provided evidences that spin-based THz emitters can be integrated and validated in target applications, such as non-destructive testing (NDT) and for THz ellipsometry measurements.
