We have constructed an electron gun that delivers highly charged femtosecond electron pulses to a target with kHz
repetition rate. Electron pulses are generated by femtosecond laser pulses in a photoemission process and are accelerated
up to 100 kV and compressed to sub-picosecond duration. Compression is essential to compensate for the space charge
effect that increases the size of electron pulses in all directions significantly. The pulses are compressed transversely by
magnetic lenses and longitudinally by the longitudinal electric field of a radio-frequency cavity. The longitudinal
compression is achieved by decelerating the electrons in the leading edge of the pulse, and accelerating the electrons in
the trailing edge of the pulse. This results in the pulse compressing and reaching the minimum pulse duration at a known
distance from the compression cavity. The short pulse duration and high repetition rate will be essential to observe subpicosecond
dynamic processes in molecules in gas phase with a good signal to noise ratio. A streak camera, consisting of
a millimeter-sized parallel plate capacitor, was used to measure the pulse duration in situ.
A two-step algorithm is developed that can reconstruct the full 3-D molecular structure from diffraction patterns of
partially aligned molecules in gas phase. This method is applicable to asymmetric-top molecules that do not need to have
any specific symmetry. This method will be important for studying dynamical processes that involve transient structures
where symmetries, if any, can possibly be broken. A new setup for the diffraction experiments that can provide enough
time resolution as well as high currents suitable for gas phase experiments is reported. Time resolution is obtained by
longitudinal compression of electron pulses by time-varying electric fields synchronized to the motion of electron pulses.