Terahertz technology is attracting growing interest for imaging, spectroscopy, high-speed communication, and information processing. However, building compact terahertz sources that can not only emit broadband radiation but also store and rewrite information remains a major challenge.
A research team has now developed a nonvolatile phase-programmable spintronic terahertz emitter based on an IrMn₃/Co₂₀Fe₆₀B₂₀/W thin-film heterostructure. In this device, femtosecond laser pulses can switch the spin polarization direction inside the emitter, thereby reversing the phase of the emitted terahertz wave.
The phase switching shows a clear laser-fluence threshold of 0.78 mJ/cm². Time-resolved double-pump measurements further reveal that the switching is driven by ultrafast laser-induced heating, with a thermal gating window of about 15 ps. This means the terahertz phase state can be programmed on an ultrafast timescale.
The device also supports a reversible write-read-reset process. High-fluence laser pulses write one nonvolatile terahertz phase state, low-fluence pulses read it out, and an external magnetic field resets the emitter to the original state. The researchers demonstrated stable operation over 30 cycles, with phase contrast remaining above 140%.
Beyond single-point switching, the team achieved spatial terahertz phase patterning. By optically writing different regions of the emitter, they produced binary terahertz patterns with a signal-to-noise ratio of 53 dB and a phase contrast of 160%.
Because the device is made from nanometer-thick sputtered metallic films, the approach is compatible with scalable fabrication and may be integrated with metasurfaces, near-field probes, and on-chip photonic systems. This work provides a promising route toward programmable terahertz sources, coded terahertz optics, and future terahertz information technologies.
