  The newly developed method of time-of-flight (ToF) momentum microscopy was
used to analyse the cold electron emission from a Cs 3D magneto-optical trap
(MOT). Three-step resonant photoionization was implemented via two intermediate
states (6P3/2 pumped with 852 nm laser and 7S1/2 with 1470 nm) and a tuneable
femtosecond Ti:sapphire laser for the final ionization step. The magnetic field
of the MOT is switched off during the photoionization step. The natural
bandwidth of the fs-laser is reduced to 4 meV using optical spectral filters.
Precise tuning of the photon energy makes it possible to observe the transition
regime between direct photoemission into the open continuum and field induced
ionization of highly-excited Rydberg states. The paths can be identified by
their characteristic dependency on the extraction field and on the Ti:sapphire
polarization. ToF analysis allowed us to disentangle the ionization paths and
the dependence of the spatio-temporal distribution of the cold electrons on the
polarization of the ionizing laser.
