  Using a blue detuned laser shaped in a Laguerre-Gaussian donut mode we highly
collimate the output of a two dimensional magneto-optical trap. The resulting
atomic beam has a 1 mm diameter, its divergence is reduced from 40 down to 3
mrad and the atomic density is increased by a factor of 200. The collimation
effect has been studied versus the order of the Laguerre-Gaussian mode (up to
10) and the laser atom frequency detuning (2 to 120 GHz). The 2D-colli-MOT
study allows us to determine the best conditions which minimize the atom
heating due to residual light absorption and optimize the collimation effect.
The 2D-colli MOT could provide a new tool to fill a 3D-MOT using lasers with
millimeter range diameters and thus sparing the laser power.
