  We describe a scheme for controlling electron injection into the quasi-linear
wakefield driven by a guided drive pulse via ionization of a dopant species by
a collinear injection laser pulse with a short Rayleigh range. The scheme is
analyzed by particle in cell simulations which show controlled injection and
acceleration of electrons to an energy of 370 MeV, a relative energy spread of
2%, and a normalized transverse emittance of 3.0 {\mu}m.
  This is an arXiv version of the original APS paper. It should be cited as N.
Bourgeois, J. Cowley, and S. M. Hooker, Phys. Rev. Lett. 111, 155004 (2013).
APS link here: http://link.aps.org/doi/10.1103/PhysRevLett.111.155004
