A collaborative research team from Peking University and Hunan University has demonstrated a novel approach to generating powerful, structured terahertz (THz) pulses with programmable polarization textures. The study, titled "Generation of Strong THz Pulses with Topologically Tunable Polarization Features", has been published in Ultrafast Science.
By driving magnetized plasma with femtosecond laser pulses, the team successfully generates Poincaré THz beams carrying both spin and orbital angular momentum. The polarization texture—including ellipticity and spatial orientation—can be precisely tuned by adjusting the angle between the magnetic field and laser propagation and by optimizing the laser spot size. Moreover, the frequency of terahertz radiation can be tuned by varying the plasma density while maintaining the topological properties of the field, enabling programmable control of vector THz radiation.
To understand the underlying mechanisms, the researchers performed large-scale three-dimensional particle-in-cell simulations supported by analytical modeling. The results show that the THz field strength can reach tens to about 150 MV/cm, sufficient to drive strong-field nonlinear phenomena. Under a transverse magnetic field, the plasma develops a spin-symmetric, bimeron-like polarization texture arising from Hermite–Gaussian mode superposition. In contrast, an axial magnetic field produces THz beams carrying both spin and orbital angular momentum, with azimuth-dependent ellipticity described by Laguerre–Gaussian modes.
"The natural anisotropy of magnetized plasmas enables us to enhance THz intensity while sculpting its polarization topology," said Prof. Xueqing Yan of Peking University.
"This scheme offers exciting opportunities for ultrafast quantum control, multidimensional nonlinear spectroscopy, and advanced material manipulation," added by Prof. Jinqing Yu from Hunan University.
