Journal
NATURE PHOTONICS
Volume 16, Issue 6, Pages 441-+Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41566-022-00995-z
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Funding
- NSF [PHY-1734215]
- DOE [DE-SC0009914, DE-SC0021190, SBIR/STTR DE-SC0017102, DE-SC0018559]
- U.S. Department of Energy (DOE) [DE-SC0017102, DE-SC0021190, DE-SC0018559] Funding Source: U.S. Department of Energy (DOE)
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The terahertz gap is a region in the electromagnetic spectrum where high power radiation sources are scarce but the demand for scientific and industrial applications is increasing. This study demonstrates the use of a circular waveguide and a strongly tapered helical undulator to efficiently extract resonant energy from a short electron beam, resulting in an average energy efficiency of about 10%.
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 similar to 10%, with some particles losing >20% of their initial kinetic energy.
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