Helical pulses – flying electromagnetic conches – were observed
image:
Figure 1：Schematic of the generation of optical and microwave helical pulses.
view moreCredit: Yijie Shen et al.
An international research team from China, Singapore, and Spain has reported the first experimental observation of helical electromagnetic pulses, a long sought form of light that twists through both space and time. Unlike conventional vortex beams, which spiral only in their spatial structure, helical pulses are single cycle wave packets whose field patterns rotate simultaneously in space and time.
The concept of helical pulses was introduced in theoretical works more than twenty years ago, but practical generation was considered extremely challenging due to the need for extreme bandwidth and precise space time coupling. The new work overcomes these barriers by developing two independent experimental routes that operate in very different frequency regimes.
In the optical domain, the researchers generated the pulses by starting from a structured parent waveform known as a toroidal pulse and then separating its internal chiral components through polarization control. Using ultrashort laser sources, metasurfaces, and polarization optics, they isolated a nearly linearly polarized helical pulse and directly visualized its characteristic twisting field through diffraction based measurements. The results reveal strong space time nonseparability and a clear three dimensional helical field structure.
In the microwave domain, the team created helical pulses by directly radiating them from a specially designed ultrawideband dual arm spiral antenna. Unlike conventional antennas, which tend to destroy delicate topological structures, the new antenna was engineered without a metallic backing and was driven by precisely tailored time domain signals. This approach produced true single cycle helical pulses whose fields display a three dimensional structure with intertwined transverse and longitudinal components. Experimental measurements, numerical simulations, and analytical theory show excellent agreement.
This achievement represents the first direct experimental confirmation of a class of electromagnetic solutions that previously existed only in theory. By showing that light and microwaves can be shaped into space time twisted, single cycle pulses, the work provides a new platform for future technologies, including ultrahigh speed communications, robust information encoding, precision imaging, particle manipulation, and the study of topological electromagnetic fields across a wide range of frequencies.
Figure 2：Spatiotemporal structure and propagation of helical pulses.
Credit
Yijie Shen et al.
Journal
Nature Communications
Article Title
Observation of helical pulses
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