Surface roughness

Optics

Physics

Brightness

Engineering

Photocathode

Electron

Physical chemistry

Transverse plane

Composite material

Beam (structure)

Ultrashort pulse

Electron gun

Atomic physics

Nuclear physics

Chemistry

Materials science

Reflection high-energy electron diffraction

Diffraction

Cathode

Laser

Quantum mechanics

Structural engineering

Surface finish

Electron diffraction

Thermal emittance

Cathode ray

Physical Review Accelerators and Beams

The performance of free electron laser x-ray light sources, and systems for ultrafast electron diffraction and ultrafast electron microscopy, is limited by the brightness of the electron sources used. The intrinsic emittance, or equivalently, the mean transverse energy (MTE) of electrons emitted from the photocathode determines the maximum possible brightness in such systems. With ongoing improvements in photocathode design and synthesis, we are now at a point where the physical and chemical surface roughness of the cathode can become a limiting factor. Here we show how measurements of the spatially dependent variations in height and surface potential can be used to compute the electron beam mean transverse energy (MTE), one of the key determining factors in evaluation of brightness.

Effects of physical and chemical surface roughness on the brightness of electron beams from photocathodes