Coherent backscattering of light from amplifying random media

We report on coherent backscattering measurements from amplifying random media using optically pumped Ti:sapphire powders. The top of the backscattering cone sharpens with increasing gain, reflecting a change in the relative contributions to the intensity from paths of different lengths. A calculation based on diffusion theory is performed on coherent backscattering from amplifying random media, which is in good agreement with the data.