First Characterization of Coherent Optical Vortices from Harmonic Undulator Radiation. Journal Name: Physical Review Letters; Journal Volume: 113; Journal Issue: 13.

摘要

We describe the experimental generation and measurement of coherent light that carries orbitalangular momentum from a relativistic electron beam radiating at the second harmonic of a helicalundulator. The measured helical phase of the light is shown to be in agreement with predictions ofthe sign and magnitude of the phase singularity, and is more than two orders of magnitude greaterthan the incoherent signal. Our setup demonstrates that such optical vortices can be produced inmodern free electron lasers in a simple afterburner arrangement for novel two-mode pump-probeexperiments.