• J.D. Jarvis, C.A. Brau, J.L. Davidson, B.L. Ivanov, J.L. Kohler
  Vanderbilt University, Nashville, TN
• H.L. Andrews
  LANL, Los Alamos, New Mexico

Recently, the theory of the Smith-Purcell free-electron laser has been confirmed by the experiments of Andrews, et al. [1], and of Gardelle, et al. [2] In addition, high-brightness cathodes have been developed using field-emission from arrays of diamond pyramids [3]. By combining these developments we have designed an ultracompact (“shirt-pocket”) free-electron laser and we have begun constructing the device. The electron beam comprises an array of 2-micron diamond-pyramid field emitters that overfills an einzel lens 200-microns wide and 1-mm long, fabricated using ps-laser machining. The beam is accelerated to 10 keV and focused in the short dimension over a lamellar metal grating with a period of 150 microns and a length of 10 mm. The predicted start current at a wavelength of {10}84 microns is 11 mA, which corresponds to 9 A/cm² at the cathode, before focusing. We have tested cathodes at 30 A/cm² and 600 mA total current; higher current density should be possible.

[1] Andrews, et al, JAP {10}5, 024904 (2009)
[2] Andrews, et al, PRST-AB 12, 080703 (2009)
[3] Gardelle, et al, PRST-AB 12, 110701 (2009)
[4] Jarvis, et al, JVSTB 27, 2264 (2009)
[5] Jarvis, Thesis, 2009

• J.D. Jarvis, C.A. Brau, J.L. Davidson, N. Ghosh, B.L. Ivanov, J.L. Kohler
  Vanderbilt University, Nashville, TN

We report recent advances in the development of electron sources of extreme brightness approaching the quantum degenerate limit. These cathodes comprise either a diamond field emitter or carbon nanotube and an individual adsorbed atom or molecule. Both emitters are covalent carbon structures and thus have the benefits of high activation energy for atomic migration, chemical inertness, and high thermal conductivity. The single adsorbate produces surface states which result in dramatic resonant enhancement of the field emission current at the allowed energies of those states. The result is a beam with a narrow energy spread that is spatially localized to roughly the size of a single atom. Thus far, we have observed short lived (~1 sec) beams from residual gases of ~6 microamps corresponding to a normalized transverse brightness of ~3·10¹⁸ A/m²-str. Whereas conventional field emitters have a quantum degeneracy of <10^-4, we estimate the degeneracy of our observed beams to be ~0.1. The use of metal adsorbates should stabilize the effect, allow higher current operation, and provide a long lived source whose brightness approaches the quantum limit.