Abstract
Nitrogen incorporated ultrananocrystalline diamond [(N)UNCD] could be an enabling material platform for injector photocathode applications due to its high emissivity. While the quantum efficiency (QE) of UNCD was reported by many groups, no experimental measurements of the intrinsic emittance/mean transverse energy (MTE) have been reported. Here, MTE measurement results for an (N)UNCD photocathode in the photon energy range from 4.41 to 5.26 eV are described. The MTE demonstrates no noticeable dependence on the photon energy, with an average value of 266 meV. This spectral behavior is shown not to be dependent upon physical or chemical surface roughness and inconsistent with low electron effective mass emission from graphitic grain boundaries but may be associated with emission from spatially confined states in the grain boundaries. The combined effect of low and constant MTE and high QE, which increases with respect to the excess laser energy, may pave the way for bright UNCD photocathodes for electron injectors.
Highlights
Nitrogen incorporated ultrananocrystalline diamond ((N)UNCD) could be an enabling material platform for photocathode applications due to its high emissivity
For a classical metal photocathode such as copper, the Fowler-Dubridge law[2] predicts that the emitted charge is a fast-growing function of excess energy, where excess energy ∆E is the difference between the laser primary incident photon energy ω and the work function φ defined as ∆E = ω−φ
To attain the highest quality electron beam metal photocathodes are often operated in the near threshold region, brightness increases with excess energy
Summary
Nitrogen incorporated ultrananocrystalline diamond ((N)UNCD) could be an enabling material platform for photocathode applications due to its high emissivity. To attain the highest quality (low divergence) electron beam metal photocathodes are often operated in the near threshold region (having the smallest ∆E, with the primary photon energy nearly matching the work function), brightness increases with excess energy.
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