• High Power Laser Science and Engineering
  • Vol. 9, Issue 4, 04000e65 (2021)
Hao Sun1、2, Xiaofan Wang3、4、*, Chao Feng5、*, Lingjun Tu1、2, Weijie Fan1、2, and Bo Liu5、*
Author Affiliations
  • 1Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai201800, China
  • 2University of Chinese Academy of Sciences, Beijing100049, China
  • 3Institute of Advanced Science Facilities, Shenzhen518000, China
  • 4Southern University of Science and Technology, College of Science, Shenzhen518055, China
  • 5Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai201210, China
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    To generate optical vortex with multiple topological charges, a simple scheme based on the phase mask shaping technique is proposed and applied in a seeded free electron laser. With a tailored phase mask, an extreme-ultraviolet (EUV) vortex with multiple topological charges can be produced. To prove the feasibility of this method, an eight-step phase mask is designed to shape the seed laser. The simulation results demonstrate that 100-MW, fully coherent EUV vortex pulses with topological charge 2 can be generated based on the proposed technique. We have also demonstrated the possibility of generating higher topological charges by using a phase mask with more steps.

    1 Introduction

    Starting from the work of Allen et al.[1], the optical vortices which carry orbital angular momentum (OAM), or light beams with spatial phase dependence of exp(i$\mathrm{\ell}\phi$), where $\phi$ denotes the azimuthal coordinate and $l$ denotes an integer referring to the topological charge, have become the subject of intense interest for numerous applications, including micromanipulation[2], detection of spinning objects[3], microscopy[4], imaging[5], optical pump schemes[6], and communication[7]. In the extreme-ultraviolet (EUV) wavelength range, the interaction of the vortex light with matter can produce special physical phenomena. Among these are the formation of Skyrmionic defects[8], the formation of charge current loops in fullerenes with an associated orbital magnetic moment[9] and the violation of dipolar selection principles during photoionization[10]. In the visible and infrared-wavelength regimes, the optical vortex could be generated by a spiral phase plate[11], the cylindrical mode converter[12], computer-generated holograms[13], and so on. At shorter wavelengths, such as in the EUV and X-ray regime, these techniques are no longer applicable because of the strong radiation damage of optical elements.