In a groundbreaking advancement that sets the stage for a new era of terahertz (THz) technology, a collaborative team of researchers from Peking University and Hunan University has pioneered a novel method for generating highly structured THz pulses with programmable polarization textures. Published recently in the prestigious journal Ultrafast Science, this study unveils the generation of Poincaré terahertz beams that carry both spin and orbital angular momentum, heralding unprecedented control over the polarization states of THz radiation and opening vast possibilities for applications in ultrafast quantum control and nonlinear optical spectroscopy.
At the core of this innovation lies a unique interaction between femtosecond laser pulses and magnetized plasma. By directing these ultra-short laser pulses into plasma affected by an external magnetic field, the researchers exploit the anisotropic nature of magnetized plasma to orchestrate intense THz radiation with remarkable topological features. This sophisticated interplay allows the precise tailoring of the polarization textures—such as ellipticity and spatial orientation—through the meticulous adjustment of the magnetic field orientation relative to the laser’s propagation direction, as well as fine-tuning the laser spot size.
A key aspect that distinguishes this approach is the ability to modulate the emitted THz frequency by varying the plasma density, all while preserving the topological characteristics of the beam’s vector field. This capacity for programmable spectral and polarization control represents a major leap forward, potentially enabling the encoding of information onto THz beams for advanced communication systems or the detailed probing of materials at ultra-fast timescales and with spatial complexity hitherto unattainable.
To deepen their understanding of this mechanism, the researchers employed extensive large-scale three-dimensional particle-in-cell (PIC) simulations, which were complemented by rigorous analytical modeling. These simulations revealed that the electromagnetic field strengths of the generated THz pulses can reach intensities on the order of tens up to approximately 150 megavolts per centimeter (MV/cm). Such formidable field strengths are sufficient to drive nonlinear optical phenomena, which could lead to novel regimes of light-matter interaction at terahertz frequencies.
The study delineates two distinct regimes based on the orientation of the applied magnetic field. When the magnetic field is transverse to the direction of laser propagation, the plasma facilitates the development of a spin-symmetric polarization texture reminiscent of a bimeron—a topological structure identified by a complex arrangement of spin directions. This emergent pattern arises from the superposition of Hermite–Gaussian modes, a class of spatial beam profiles characterized by distinct symmetry and node structures.
Conversely, orienting the magnetic field axially along the laser propagation direction engenders THz beams that exhibit rich topological complexity by simultaneously carrying both spin and orbital angular momentum. In this scenario, the ellipticity of the polarization varies azimuthally around the beam axis, a behavior accurately described by Laguerre–Gaussian modes. These modes are well-known for their doughnut-shaped intensity profiles and their capacity to carry orbital angular momentum, making them invaluable tools in the realms of optical manipulation and quantum information.
Prof. Xueqing Yan from Peking University, contributing to the study, emphasized the natural advantage provided by the anisotropy of magnetized plasmas, stating that this innate property not only enhances the intensity of the emitted THz radiation but also facilitates the precise sculpting of its polarization topology. This dual capability elevates magnetized plasma as a versatile and powerful medium for THz generation, diverging from traditional planar or homogeneous sources.
The implications of this technology are vast. With the ability to produce structured THz pulses with dynamic, programmable polarization states, researchers and engineers could potentially harness these beams for ultrafast quantum control schemes, where manipulating quantum states on femtosecond timescales requires exquisite command over the electromagnetic field configurations. Furthermore, the approach opens pathways for multidimensional nonlinear spectroscopy techniques, allowing scientists to interrogate complex materials and biological systems with new degrees of sensitivity and selectivity.
Prof. Jinqing Yu of Hunan University highlighted the transformative potential of this breakthrough. By enabling topological tuning of THz field vectors, the method promises to revolutionize advanced material manipulation, providing tools to engineer novel properties in matter through the precise orchestration of light-matter interactions. This could lead to the development of next-generation devices in optoelectronics, quantum computing, and biophotonics.
The combination of experimental precision, robust theoretical backing, and computational validation in this work establishes a strong foundation for further exploration of magnetized plasma-based THz sources. As the demand for THz technologies grows—particularly in high-resolution imaging, wireless communications, and spectroscopy—the ability to engineer the polarization and topological structures of THz pulses will be a critical enabler of new functionalities.
What sets this research apart is not only its demonstration of intense THz field generation but also its flexible control over the beam’s vectorial properties. Typically, THz sources have been limited to fixed polarization states or unstructured radiation, constraining their applicability in advanced photonic systems. The present study’s insight into leveraging Hermite–Gaussian and Laguerre–Gaussian mode superpositions highlights a sophisticated level of beam engineering that opens new frontiers for science and technology.
Looking forward, integrating this plasma-based THz source with existing photonic and electronic systems could usher in hybrid platforms capable of bridging optical and electronic domains with unprecedented efficacy. The high field strengths and tunable polarization landscapes could be instrumental in driving nonlinear processes such as high-harmonic generation, parametric amplification, or THz-driven electron dynamics in materials.
In summary, this pioneering work crosses the boundaries of plasma physics, laser science, and nonlinear optics, delivering an innovative approach to shaping terahertz radiation with topologically tunable polarization features. It paves the way for next-generation THz technologies that promise enhancements in fundamental research and practical applications alike, reinforcing the central role of magnetized plasmas as a fertile playground for light–matter interaction at extreme frequencies and intensities.
Subject of Research: Not applicable
Article Title: Generation of strong THz pulse with topologically tunable polarization feature
News Publication Date: 3-Sep-2025
Web References:
10.34133/ultrafastscience.0116
References:
Generation of Strong THz Pulses with Topologically Tunable Polarization Features, Ultrafast Science, DOI: 10.34133/ultrafastscience.0116
Image Credits: Ultrafst Science
Keywords
Plasma physics, Laser pulses
