Femto-seconds electron beam diffraction using photocathode RF gun

One of the 21^st century scientific frontiers is to explore the molecule structure transition in the femto-second time scale. X-ray free electron laser (XFEL) is one of the tools now under development for investigating femto-second structure transition. We are proposing an alternative technique femto-second electron diffraction based on the photocathode RF gun. We will present a design of a kHz femto-seconds electron diffraction system based on the photocathode RF gun. Our simulation shows that, photocathode RF gun can produce 100 fs (FWHM) electron bunch with millions electrons at about 2 MeV. This is at least one order of magnitude reduction in bunch length, and two orders of magnitude increase in number of electrons comparing to present DC electron diffraction system. We will also discuss various issues and limitations related to MeV electron diffraction.