  Atoms can scatter light and they can also amplify it by stimulated emission.
  From this simple starting point, we examine the possibility of realizing a
random laser in a cloud of laser-cooled atoms. The answer is not obvious as
both processes (elastic scattering and stimulated emission) seem to exclude one
another: pumping atoms to make them behave as amplifier reduces drastically
their scattering cross-section. However, we show that even the simplest atom
model allows the efficient combination of gain and scattering. Moreover,
supplementary degrees of freedom that atoms offer allow the use of several gain
mechanisms, depending on the pumping scheme. We thus first study these
different gain mechanisms and show experimentally that they can induce
(standard) lasing. We then present how the constraint of combining scattering
and gain can be quantified, which leads to an evaluation of the random laser
threshold. The results are promising and we draw some prospects for a practical
realization of a random laser with cold atoms.
