  When considering particles produced in reactive plasmas, their basic
properties, such as refractive index and grain size often need to be known.
They can be constrained both ex-situ, e.g., by microscopy, and in-situ by
polarimetry, i.e., analyzing the polarization state of scattered light.
Polarimetry has the advantage of temporal resolution and real-time measurement,
but the analysis is often limited by the assumption of single scattering and
thus optically thin dust clouds. This limits the investigation of the growth
process typically to grain sizes smaller than about 200 nm. Using 3D polarized
radiative transfer simulations, however, it is possible to consider multiple
scattering and to analyze the properties of dense particle clouds.
  We study the impact of various properties of dust clouds on the scattering
polarization, namely the optical depth of the cloud, the spatial density
distribution of the particles, their refractive index as well as the particle
size dispersion. We find that ambiguities can occur regarding optical depth and
spatial density distribution as well as regarding refractive index and particle
size dispersion. Determining the refractive index correctly is especially
important as it has a strong impact on the derived particle sizes. With this
knowledge, we are able to design an in-situ diagnostics strategy for the
investigation of the particle growth process based on radiative transfer
simulations which are used to model the polarization over the whole growth
process. The application of this strategy allows us for the first time to
analyze the polarization measured during a growth experiment in a reactive
argon-acetylene plasma for particle radii up to 280 nm.
