Characterization of Cs3Sb photocathodes at cryogenic temperatures

We report measurements of quantum efficiency (QE) and mean transverse energy (MTE) from Cs3Sb photocathodes in a wide range of photon energies at both room and cryogenic temperatures. Our measurements show a strong temperature dependence of MTE even at photon energies well above threshold, indicating the presence of strong inelastic scattering of excited electrons during transport before emission into vacuum. We also demonstrate a cathode cooling method that largely preserves the QE while reducing MTE, allowing us to achieve MTEs as low as 58 meV with 3% QE in green light from Cs3Sb photocathodes. Our results are crucial for producing brighter electron beams for various photoinjector applications like ultrafast electron diffraction and microscopy, x-ray free-electron lasers, and particle colliders.