Lowest mean transverse energy obtainable from a photocathode
In plain words
Electrons leave a cathode with some random sideways energy that blurs the beam; how low it can go, and what sets the floor, is open.
Precise statement
The intrinsic normalized emittance of a photoemission source is eps_n = $\sigma_x$ sqrt(MTE/(m c^2)), with sigma_x the rms source size and MTE the mean transverse energy of emitted electrons. Values of approximately $5\,\mathrm{meV}$ were reported around 2020 from near-threshold photoemission of cryogenically cooled single-crystal Cu(100). Determine the lowest achievable MTE at quantum efficiency $\ge 10^{-5}$ and the physics that sets it (lattice temperature, surface roughness and work-function variation, electron-phonon and electron-electron scattering, multiphoton emission).
What would settle it
MTE measurements versus temperature, photon energy and surface preparation on candidate cathodes, matched by a photoemission model including the surface.
Parent problems
- Special case of Fundamental trade-off between quantum efficiency and mean transverse energy · open · from revision 1 Minimum MTE at QE above 1e-5 is one point of the MTE-QE bound The parent was revised since revision 1: it now states another question.
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