Spatiotemporal shaping of broadband helical light pulses at relativistic intensities

Abstract

Spatiotemporal control of laser pulses at relativistic field strengths is a long-standing goal in laser–plasma interactions and extreme-field science. Helical wavepackets that couple spectral and orbital angular momentum (OAM) modes produce rotating intensity distributions, often referred to as light springs. Here we demonstrate the generation of light springs at relativistic intensities, reaching peak values above 1.4 × 1018 W cm−2, using a scalable and high-power-compatible optical architecture. By spectrally separating a broadband high-power pulse, imprinting distinct helical phases using off-axis spiral phase mirrors, and coherently recombining the components with engineered dichroic optics, we realize controlled spatiotemporal OAM in a geometry compatible with large-scale laser facilities. Hyperspectral imaging combined with off-axis holography enables full spatiotemporal reconstruction of the focal fields, revealing tunable transverse rotation. Furthermore, controlled spectral chirp allows manipulation of the temporal evolution of the transverse mode structure. These results establish a scalable route to relativistic light fields with tailored spatiotemporal OAM and provide new opportunities for structured laser–plasma interactions. Researchers demonstrate the generation of helical intensity wavepackets at relativistic intensities, reaching peak values above 1.4 × 1018 W cm−2. Controlled spatiotemporal orbital angular momentum, in a geometry compatible with large-scale laser facilities, is realized.