500-FS PHOTOELECTRON GUN FOR TIME-RESOLVED ELECTRON-DIFFRACTION EXPERIMENTS

A photoelectron gun as a source of a photoinduced, monoenergetic (ener gy spread < 0.5 eV), well-collimated (divergence < 0.5 deg), sharp (di ameter < 0.7 mm at the 1/e level), and ultrashort (less than or equal to 500 fs) bunch of Electrons to be used for time-resolved electron di ffraction (TRED) experiments is computer designed, assembled, and test ed. 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 focus ed onto a solid state target chosen from a set of interchangeable targ ets. High temporal resolution enables measurement with femtosecond pre cision of the diffraction pattern perturbation after the exiting laser radiation drops onto a target. Demonstration experiments with a 300-A ngstrom Al target in transmission-type mode result in diffraction imag es of reasonable quality under accumulation of up to 4 x 10(4) 500-fs photoelectron pulses. (C) 1998 Society of Photo-Optical Instrumentatio n Engineers.