Femtosecond Photocathode Electron Source*

A photocathode-based low-emittance femtosecondbunch electron source is developed in Osaka University to reveal the hidden dynamics of intricate molecular and atomic processes in materials through experimentation such as time-resolved pulse radiolysis or time-resolved electron diffraction. The transverse and longitudinal dynamics of femtosecond electron beam in the photocathode rf gun were studied by particle simulation. The growths of the emittance, bunch length and energy spread due to the rf effect and the space charge effect were investigated by changing the laser injection phase, the laser parameters and the bunch charge. The beam simulation indicates that a sub-100-fs MeV electron source with the normalized transverse emittance of 0.1 mm-mrad and the relative energy spread of 10~10 at bunch charge of 0.1-1 pC is achievable in the rf gun driven by a femtosecond laser light.