Isotropization time for non-Markovian CTRWs

We calculate the mean-squared displacement, , for a CTRW taking into account effects of anisotropic turn angles. When the pausing-time density is a negative exponential one finds a simple expression for which allows an exact determination of the transition time from ballistic to diffusive motion. In the non-Markovian case an exact expression is obtained for the Laplace transform of . The results are useful in the analysis of photon migration in a turbid medium.