Short Laser Pulse Twists Light into a 3D Corkscrew express
A sharp tug on a twisted cord sends a spiral wave along it. Similarly, an ultrashort laser flash in a RhSi crystal gives birth to light instantly twisted into a three-dimensional corkscrew. This is a manifestation of high-harmonic generation: like a powerful pinch makes electrons jump higher and, as they fall back, emit many colors at once — from red to X-rays.
The RhSi crystal itself is already a twisted cord: its atomic lattice is twisted like a screw and can be 'right-handed' or 'left-handed'. This asymmetry gives the emerging light a strictly defined rotation. Inside it, Weyl fermions behave like massless particles, promising electronics based on twisted beams rather than currents.
The idea stems from Charles Townes, the inventor of the laser. Now physicists control the shape of the light wave in attoseconds — a billion times faster than a camera shutter. An unexpected bonus: such a 'light spring' can encode data by the direction of its coils, doubling the information capacity.
Original abstract
as written by the authors arXiv:2603.05346
High harmonic generation (HHG) in solids results from an interplay between intraband acceleration and electron-hole recombination driven by a high-intensity laser pulse. Here, we theoretically reveal that the driving pulse duration can play a major role in extending HHG to higher photon energies by promoting higher conduction band excitations. The effect is present in a conventional semiconductor as Si, restricted in a large-gap insulator as MgO, and most prominent in RhSi, a prototypical chiral Weyl semimetal presenting numerous band crossings. Further, we elucidate the HHG selection rules in RhSi required for the synthesis of attosecond locally chiral light. The chiral crystal structure enables the generation of a local 3D electric field exhibiting an asymmetric instantaneous torsion on attosecond timescales. A pronounced circular dichroism emerges when the driving helicity is either aligned with or opposite to the crystal handedness. Our findings motivate future experiments in chiral Weyl semimetals to track high-energy band crossings and in-situ locally chiral light, paving the way for chiral compact light sources and light-wave driven topological electronics.
Like left and right hands, the RhSi crystal does not match its mirror image, and this 'teaches' light to twist in only one direction.
In Stanisław Lem's 'Solaris,' the ocean generated asymmetric structures; here, the asymmetric crystal itself twists light — almost like a sentient material.