Ultracold Electrons via Near-Threshold Photoemission from Single-Crystal Cu(100)

Area of Science:

• * Physics
• * Materials Science
• * Electron Optics

Background:

• * Low electron transverse energy is crucial for next-generation compact X-ray free electron lasers (XFELs).
• * Ultrafast electron diffraction, spectroscopy, and microscopy demand high-quality electron beams.
• * Existing electron sources have limitations in energy spread and transverse energy.

Purpose of the Study:

• * To demonstrate a record low mean transverse energy from a photocathode.
• * To achieve the smallest electron energy spread for advanced applications.
• * To investigate the physics limiting electron energy spread.

Main Methods:

• * Employed near-threshold photoemission from a cryo-cooled (100) copper surface.
• * Utilized advanced measurement techniques to determine electron transverse energy and energy spread.
• * Analyzed the influence of temperature and vacuum density of states on electron emission.

Main Results:

• * Demonstrated a record low mean transverse energy of 5 meV.
• * Achieved an electron energy spread of less than 11.5 meV.
• * Established a new benchmark for electron source performance, exceeding existing technologies by over an order of magnitude.

Conclusions:

• * Cryo-cooled copper surfaces enable unprecedented low electron transverse energy and energy spread.
• * The demonstrated electron source is ideal for compact XFELs and ultrafast electron experiments.
• * Electron energy spread at the meV scale is fundamentally limited by temperature and vacuum density of states.