  The full three-dimensional photoelectron momentum distributions of argon are
measured in intense near-circularly polarized laser fields. We observed that
the transverse momentum distribution of ejected electrons by 410-nm
near-circularly polarized field is unexpectedly narrowed with increasing laser
intensity, which is contrary to the conventional rules predicted by adiabatic
theory. By analyzing the momentum-resolved angular momentum distribution
measured experimentally and the corresponding trajectories of ejected electrons
semiclassically, the narrowing can be attributed to a temporary trapping and
thereby focusing of a photoelectron by the atomic potential in a quasibound
state. With the near-circularly polarized laser field, the strong Coulomb
interaction with the rescattering electrons is avoided, thus the Coulomb
focusing in the retrapped process is highlighted. We believe that these
findings will facilitate understanding and steering electron dynamics in the
Coulomb coupled system.
