  High resolution near-infrared adaptive optics imaging and polarimetry have
been obtained of the Homunculus Nebula and its central star Eta Carinae (HD
93308). Maps of the linear polarization at a resolution of <0.2'' have been
made in the J, H and K bands and in a narrow 2.15micron continuum band (K_c).
The overall appearance of the nebula in the near-IR is similar in all bands and
to that at V, with specific features less sharp to longer wavelengths. The
large-scale pattern of polarization vectors is centro-symmetric demonstrating
that single scattering dominates everywhere except perhaps in the central
bright core. Polarization maps at K_c in the near vicinity of Eta Carinae were
restored using a PSF derived from blind deconvolution. An extension of the flux
in the direction of the optically visible speckle knots was detected, with 18%
polarization determined for one knot.
  The most remarkable result of the linear polarization mapping is the level of
similarity in the spatial structure, and the degree of polarization, between
the near-IR and optical data. Such a polarization pattern cannot arise in Mie
scattering from a single power law distribution of grain sizes unless the
particles are very small compared with the wavelength, in disagreement with
mid-IR observations. The colour dependence of the extinction was found to be
shallower than the typical ISM, indicating the presence of large grains.
Optical depth effects and a broad distribution in grain sizes are suggested to
explain these contradictory results, perhaps with a dependence of the grain
size with depth into the small obscuring clouds in the Homunculus lobes.
However the presence of aligned grains, previously inferred from mid-IR
polarization, may also affect the dust-scattered radiation. (Abridged abstract)
