  We demonstrate experimentally that a polarized nuclear spin modifies the
dynamic behavior of a neighboring electronic spin. Specifically, an
out-of-phase component appears in the electronic spin-echo signal. This
component is proportional to the nuclear spin degree of polarization and
strongly depends on the nuclear polarization direction. When the electronic
spin is surrounded by a polarized nuclear spin bath, the spin-echo quadrature
manifests a characteristic frequency related only to the nuclear spins
abundance and their collective polarization. We use this analysis to propose a
novel measurement method for the local nuclear spin bath of a single electronic
spin. We quantify the realistic experimental regimes at which the scheme is
efficient. Our proposal has potential applications for quantum sensing schemes,
and opens a route for a systematic study of polarized mesoscopical-systems.
