Summary of the working group on transverse emittance from photocathodes

As the wavelength of the FEL decreases, so does the acceptable emittance of the electron beam entering the wiggler. Eventually, the emittance of the electrons as they leave the cathode begins to play a dominant role. The task facing the working group was to estimate the lowest emittance attainable as they escape the surface. The emittance of these electrons are dictated by many factors including the kinetic energy imparted to them by the photons, the extraction and optical field and the temperature of the electrons and the lattice. Maximum contribution due to each of these effects are estimated in the following section