Abstract
We have developed a photocathode dc gun for a compact Smith-Purcell free-electron laser in the terahertz wavelength region. The gun system consists of an alkali antimonide photocathode preparation chamber, a dc gun with a 250 kV-50 mA Cockcroft-Walton high-voltage power supply, and a downstream beamline with a water-cooled beam dump to accommodate a beam power of 5 kW. We fabricated a Cs3Sb photocathode with quantum efficiency of 5.8% at a wavelength of 532 nm and generated a 150 keV beam with current of up to 4.3 mA with a 500 mW laser. A vacuum chamber for the Smith-Purcell free-electron laser has been installed in the downstream beamline. We describe the present status of our work.
Highlights
The superradiance of Smith-Purcell (SP) emissions was first observed in 1998 at wavelengths of 300–900 μm using an electron beam propagating just above a grating at energy of 20–40 keV [1]
They proposed an SP free-electron laser (FEL) theory in which evanescent waves induced on the grating surface contribute to the formation of electron microbunching spaced at the evanescent wavelength
The fundamental wavelength of the evanescent wave is longer than the SP radiation wavelength, and coherent SP radiation occurs only at the higher harmonics
Summary
The superradiance of Smith-Purcell (SP) emissions was first observed in 1998 at wavelengths of 300–900 μm using an electron beam propagating just above a grating at energy of 20–40 keV [1]. The superradiant SP radiation was theoretically studied by Andrews and Brau [2,3] They proposed an SP free-electron laser (FEL) theory in which evanescent waves induced on the grating surface contribute to the formation of electron microbunching spaced at the evanescent wavelength. The evanescent wavelength was experimentally verified to be longer than that of the SP radiation, and coherent SP radiation at the second and third harmonics of the evanescent waves was observed [4,5] These theoretical and experimental studies promise a compact, high-power terahertz (THz) light source based on the SP FEL technique. We added an alkali antimonide photocathode preparation system to the gun system because alkali antimonide has a longer lifetime than GaAs and is more appropriate for high-current beam applications [7].
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