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Updated: Feb 23, 2026

An Experimental Protocol for Femtosecond NIR/UV - XUV Pump-Probe Experiments with Free-Electron Lasers
Published on: October 23, 2018
Observation of an optical vortex beam from a helical undulator in the XUV region
Tatsuo Kaneyasu1, Yasumasa Hikosaka2, Masaki Fujimoto3
1Saga Light Source, Tosu 841-0005, Japan.
Abstract:
The observation of an optical vortex beam at 60 nm wavelength, produced as the second-harmonic radiation from a helical undulator, is reported. The helical wavefront of the optical vortex beam was verified by measuring the interference pattern between the vortex beam from a helical undulator and a normal beam from another undulator. Although the interference patterns were slightly blurred owing to the relatively large electron beam emittance, it was possible to observe the interference features thanks to the helical wavefront of the vortex beam. The experimental results were well reproduced by simulation.
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