  We investigate, both numerically and analytically, the time evolution of a
particle in an initial plane wave state as it is subject to elastic scattering
in a two-dimensional disordered system with Rashba spin-orbit coupling (SOC).
In the analytic calculation, we treat the SOC non-perturbatively, and the
disorder perturbatively using the Diffuson and the Cooperon. We calculate the
time dependence of coherent backscattering (CBS) as a function of the strength
of the SOC. We identify weak and strong SOC regimes, and give the relevant time
and energy scales in each case. By studying the time dependence of the
anisotropy of the disorder-averaged momentum distribution we identify the spin
relaxation time. We find a crossover from D'yakonov-Perel' spin relaxation for
weak SOC to Elliot-Yafet like behaviour for strong SOC.
