Much of
the theory and experimentation concerning creation of a high-brightness
electron beam from a photocathode, and then applying emittance compensation
techniques, assumes that one must strive for a uniform density electron
beam, having a cylindrical shape. On the other hand, this shape has
large nonlinearities in the space-charge field profiles near the beam?s
longitudinal extrema. These nonlinearities are known to produce both
transverse and longitudinal emittance growth. On the other hand, it
has recently been shown by Luiten that by illuminating the cathode with
an ultra-short laser pulse of appropriate transverse profile, a uniform
density, ellipsoidally shaped bunch is dynamically formed, which then
has linear space-charge fields in all dimensions inside of the bunch.
We study here this process, and its marriage to the standard emittance
compensation scenario that is implemented in most recent photoinjectors.
It is seen that the two processes are compatible, with simulations indicating
a very high brightness beam can be obtained. Progress towards an experimental
test of this scheme are discussed in a companion talk.