  We quantify the entanglement generated between an atom and a laser pulse in
free space. We find that the entanglement calculated using a simple
closed-system Jaynes-Cummings Hamiltonian is in remarkable agreement with a
full open-system calculation, even though the free-space geometry is far from
the strong coupling regime of cavity QED. We explain this result using a simple
model in which the atom couples weakly to the laser while coupling strongly to
the vacuum. Additionally we place an upper bound on the total entanglement
between the atom and all paraxial modes using a quantum trajectories
unravelling. This upper bound provides a benchmark for atom-laser coupling.
