  Plasma based acceleration is considered a promising concept for the next
generation of linear electron-positron colliders. Despite the great progress
achieved over last twenty years in laser technology, laser and beam driven
particle acceleration, and special target availability, positron acceleration
remains significantly underdeveloped if compared to electron acceleration. This
is due to both the specifics of the plasma-based acceleration, and the lack of
adequate positron sources tailored for the subsequent plasma based
acceleration. Here a positron source based on the collision of a high energy
electron beam with a high intensity laser pulse is proposed. The source relies
on the subsequent multi-photon Compton and Breit-Wheeleer processes to generate
an electron-positron pair out of a high energy photon emitted by an electron.
Due to the strong dependence of the Breit-Wheeler process rate on photon energy
and field strength, positrons are created with low divergence in a small volume
around the peak of the laser pulse. The resulting low emittance in the
submicron range potentially makes such positron source interesting for collider
applications.
