  We report optical imaging, optical and near-infrared polarimetry, and Spitzer
mid-infrared spectroscopy of comet C/2007 N3 (Lulin). Polarimetric observations
were obtained in R (0.676 micron) at phase angles from 0.44 degrees to 21
degrees with simultaneous observations in H (1.65 micron) at 4.0 degrees,
exploring the negative branch in polarization. Comet C/2007 N3 (Lulin) shows
typical negative polarization in the optical as well as a similar negative
branch near-infrared wavelengths. The 10 micron silicate feature is only weakly
in emission and according to our thermal models, is consistent with emission
from a mixture of silicate and carbon material. We argue that large,
low-porosity (akin to Ballistic Particle Cluster Aggregates) rather absorbing
aggregate dust particles best explain both the polarimetric and the
mid-infrared spectral energy distribution.
