  We demonstrate the versatility of a dual imaging polarimeter working in
tandem with a Lyot coronagraph and Adaptive Optics to suppress the highly
static speckle noise pattern--the greatest hindrance to ground-based direct
imaging of planets and disks around nearby stars. Using a double difference
technique with the polarimetric data, we quantify the level of speckle
suppression, and hence improved sensitivity, by placing an ensemble of
artificial faint companions into real data, with given total brightness and
polarization. For highly polarized sources within 0.5 arcsec, we show that we
achieve 3 to 4 magnitudes greater sensitivity through polarimetric speckle
suppression than simply using a coronagraph coupled to a high-order Adaptive
Optics system. Using such a polarimeter with a classical Lyot coronagraph at
the 3.63m AEOS telescope, we have obtained a 6.5 sigma detection in the H-band
of the 76 AU diameter circumstellar debris disk around the star HR 4796A. Our
data represent the first definitive, ground-based, near-IR polarimetric image
of the HR 4796A debris disk and clearly show the two outer ansae of the disk,
evident in Hubble Space Telescope NICMOS/STIS imaging. We derive a lower limit
to the fractional linear polarization of 29% caused by dust grains in the disk.
In addition, we fit simple morphological models of optically thin disks to our
data allowing us to constrain the dust disk scale height to 2.5{+5.0}_{-1.3} AU
and scattering asymmetry parameter (g=0.20^{+.07}_{-.10}). These values are
consistent with several lines of evidence suggesting that the HR 4796A disk is
dominated by a micron-sized dust population, and are indeed typical of disks in
transition between those surrounding the Herbig Ae stars to those associated
with Vega-like stars.
