  We present a new and efficient implementation of Raman cooling of trapped
atoms. It uses Raman pulses with an appropriate frequency chirp to realize a
velocity selective excitation through a rapid adiabatic passage. This method
allows to address in a single pulse a large number of non zero atomic velocity
classes and it produces a nearly unity transfer efficiency. We demonstrate this
cooling method using cesium atoms in a far-detuned crossed dipole trap.
Three-dimensional cooling of $1 \times 10^{5}$ atoms down to $2 \mu$K is
performed in 100 ms. In this preliminary experiment the final atomic density is
$1.3\times 10^{12}$ at/cm$^3$ (within a factor of 2) and the phase-space
density increase over the uncooled sample is 20. Numerical simulations indicate
that temperatures below the single photon recoil temperature should be
achievable with this method.
