Photoinjector

[5][6] High-brightness electron beams produced by photoinjectors are used directly or indirectly to probe the molecular, atomic and nuclear structure of matter for fundamental research, as well as material characterization.

The key component of a photoinjector is a photocathode, which is located inside the cavity of electron gun (usually, a 0.6-fractional cell for optimal distribution of accelerating field).

For that reason, photoelectron guns often have one or more full-size booster cells to increase the beam energy and reduce the space-charge effect.

Semiconductor cathodes are often sensitive to ambient conditions and might require a clean preparation chamber located behind the photoelectron gun.

For example, a fs-scale laser pulse with an elliptical transverse profile creates a thin "pancake" electron bunch, that evolves into a uniformly filled ellipsoid under its own space-charge fields.

Animation showing how an AC linear accelerator works. For a photoinjector, the source S is the cathode inside the fractional cell, followed by four booster cells of RF field.