  Debris disks give us the unique opportunity to probe the properties of small
$\mu$m-sized particles, allowing us to peer into the constituents of their
parent bodies, young analogs of comets and asteroids of our solar system. In
the past, studies of the total intensity phase function have proven powerful to
constrain the main characteristics of the dust particles in debris disks.
Nonetheless, there can remain some degeneracies in the modeling that can be
alleviated when considering polarized intensity observations. We obtained new
near-IR scattered light observations of four young debris disks which allow us
to constrain the degree of linear polarization as a function of the scattering
angle. All four debris disks are detected in polarized intensity, and three are
also recovered in total intensity. We measured peak degree of polarization of
$\lesssim 40$\% for all three disks. We find that the particles must consist of
highly refractive and absorbing material. For HD129590, by measuring the
polarization fraction beyond the birth ring, we constrain the width of the size
distribution to be smaller and smaller, compatible with the effect of radiation
pressure. We put these findings to the test and present a self-consistent
approach to produce synthetic images, assuming different profiles for the
radiation pressure strength, and accounting for the presence of unbound grains.
We find the contribution of these grains to be especially critical to reproduce
the increasing degree of polarization with stellocentric distances. Some of our
results might seem difficult to reconcile with our understanding of cosmic dust
but since similar results have been obtained for other disks, we discuss the
current limitation of available light scattering models as well as possible
avenues to alleviate these unfortunate limitations.
