Way to Generate OAM Pulses in UV Range Could Help in Materials Research

Scientists from the Skolkovo Institute of Science and Technology (Skoltech), in collaboration with researchers from the Shanghai Institute of Optics and Fine Mechanics and the Helmholtz Institute, have proposed a way to generate intense, short, twisted pulses in the ultraviolet (UV) range to aid scientists in their investigation of new materials.

Although optical angular momentum (OAM) beams can be readily derived from Gaussian laser beams with phase plates or gratings, achieving OAM is more challenging in the extreme ultraviolet (XUV) range. The Skoltech team theoretically and numerically demonstrated that intense surface harmonics carrying OAM can be naturally produced by the intrinsic dynamics of a relativistically intense, circularly polarized Gaussian beam (i.e., nonvortex) interacting with a target at normal incidence.

OAM pulse wavefront. Courtesy of Skoltech.

Relativistic surface oscillations convert the laser pulses to intense XUV harmonic radiation via the relativistic oscillating mirror mechanism. The researchers showed that the azimuthal and radial dependence of the harmonic generation process converted the spin angular momentum of the laser beam to OAM, resulting in an intense attosecond pulse with OAM.

The ability to generate intense OAM pulses in the UV range could facilitate the development of new materials at characteristic spatial (tens of nanometers) and temporal (hundreds of attoseconds) scales. Such high-resolution visualizations could be used to study and predict materials’ properties. Visible or IR-range electromagnetic pulses with angular momentum capability are already used in telecommunications to increase the data transfer capacity of fiber optic networks, the researchers said.

“We can apply the term ‘UV vortices’ to the pulses we obtained through mathematical modeling,” professor Sergey Rykovanov said. “Along with twisted wavefronts, our pulses have a duration of a few hundred attoseconds only — a temporal scale typical for atomic physics. For comparison, an electron makes one ‘revolution’ in a hydrogen atom within a hundred attoseconds or so.”

The scientists used supercomputers, including the Zhores supercomputer installed at Skoltech, to ensure realistic 3D simulation of the UV vortex effect. Currently, the team is preparing for the “vortex search” experiment. The scientists believe that the generation of intense, attosecond UV vortices could open new possibilities in the study of electrons’ motion dynamics in various materials and condensed matter.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-019-13357-1).