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Single-pass high-efficiency terahertz free-electron laser

Nature Photonics volume 16, pages 441–447 (2022)Cite this article

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Abstract

The terahertz gap is a region of the electromagnetic spectrum where high average and peak power radiation sources are scarce while at the same time scientific and industrial applications are growing in demand. Free-electron laser (FEL) coupling in a magnetic undulator is one of the best options for radiation generation in this frequency range, but slippage effects require the use of relatively long and low-current electron bunches to drive the terahertz FEL, limiting amplification gain and output peak power. Here we use a circular waveguide in a 0.96-m strongly tapered helical undulator to match the radiation and electron-beam velocities, allowing resonant energy extraction from an ultrashort 200-pC 5.5-MeV electron beam over an extended distance. Electron-beam spectrum measurements, supported by energy and spectral measurement of the terahertz FEL radiation, indicate an average energy efficiency of ~10%, with some particles losing >20% of their initial kinetic energy.

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Fig. 1: Tapering-enhanced zero-slippage terahertz FEL scheme.
Fig. 2: Electron beam and THz energy measurements.
Fig. 3: Interferometry measurements.
Fig. 4: THz FEL simulations.

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Data availability

The datasets for the beam energy spectrum as a function of charge and the interferometry scans at different beam energies are available from the corresponding author upon reasonable request.

Code availability

The GPT input file for simulating the entire Pegasus beamline, including the gun, the RF buncher linac and the interaction with the TE11 mode in the undulator, is available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by NSF grant no. PHY-1734215 and DOE grants nos. DE-SC0009914 and DE-SC0021190. The undulator construction was carried out under SBIR/STTR DE-SC0017102 and DE-SC0018559.

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Authors and Affiliations

  1. UCLA Department of Physics and Astronomy, Los Angeles, CA, USA

    A. Fisher, Y. Park, M. Lenz, A. Ody & P. Musumeci

  2. RadiaBeam Technologies, Santa Monica, CA, USA

    R. Agustsson, T. Hodgetts & A. Murokh

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  1. A. Fisher
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  8. P. Musumeci
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Contributions

A.F. and Y.P. carried out the measurements and analysed the data. M.L. and A.O. helped with UCLA Pegasus beamline operation, including alignment, vacuum and controls. P.M. proposed and supervised the experiment. A.M. participated in the TESSA development and is the principal investigator on one of the supporting grants. R.A. and T.H. were responsible for the undulator construction. A.F., Y.P. and P.M. prepared the manuscript, which was revised and edited by all co-authors.

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Correspondence to A. Fisher, Y. Park or P. Musumeci.

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The authors declare no competing interests.

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Nature Photonics thanks Lixin Yan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Fisher, A., Park, Y., Lenz, M. et al. Single-pass high-efficiency terahertz free-electron laser. Nat. Photon. 16, 441–447 (2022). https://doi.org/10.1038/s41566-022-00995-z

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