500-fs photoelectron gun for time-resolved electron diffraction experiments

A photoelectron gun as a source of a photoinduced, monoen- ergetic (energy spread ,0.5 eV), well-collimated (divergence ,0.5 deg), sharp (diameter ,0.7 mm at the 1/e level), and ultrashort (<500 fs) bunch of electrons to be used for time-resolved electron diffraction (TRED) experiments is computer designed, assembled, and tested. In single-shot mode, it generates up to 10 3 of 30 keV electrons, and the electron pulse can be either measured in streak mode or focused onto a solid state target chosen from a set of interchangeable targets. High temporal resolution enables measurement with femtosecond precision of the diffraction pattern perturbation after the exiting laser radiation drops onto a target. Demonstration experiments with a 300-A A1 target in transmission-type mode result in diffraction images of reasonable quality under accumulation of up to 4310 4 500-fs photoelectron pulses.