  The widely-used Jones and Mueller differential polarization calculi allow
non-depolarizing deterministic polarization interactions, known to be elements
of the $SO^+(1,3)$ Lorentz group, to be described in an efficient way. In this
Letter, a stochastic differential Jones formalism is shown to provide a clear
physical insight on light depolarization, which arises from the interaction of
polarized light with a random medium showing fluctuating anisotropic
properties. Based on this formalism, several "intrinsic" depolarization metrics
naturally arise to efficiently characterize light depolarization in a medium,
and an irreversibility property of depolarizing transformations is finally
established.
