Measured Degree of Infrared Polarization for a Variety of Thermal Emitting Surfaces

Abstract : We report on a series of parametric measurements designed to measure the attenuative effects that surface roughness and aerosol contamination play in reducing polarized thermal surface emission. In particular, we measure the spectrally resolved linear degree of polarization (LDOP) for a series of roughened borosilicate (Pyrex trade mark) glass substrates as a function of roughness parameter, Ra, root mean square slope, m, and the angle of observation, theta. Spectrally resolved LDOP is measured over the waveband region 4 to 13 micrometers by a modified Fourier transform IR spectrometer in which a wire-grid polarizer and an achromatic quarter-wave plate are used in conjunction to measure all four Stokes parameters. A second set of measurements is conducted on similar smooth glass substrates that are subjected to varying degrees of dew formation and aerosol contamination. Test substrates are oriented at a high grazing angle of 80 degrees and placed in a closed chamber. Dew or attenuative particulates, i.e., carbon black, potassium bromide, or pollen particles, are allowed to condense/settle on the thermal emitting surface while a band-averaged LDOP is recorded with a long-wave polarimetric IR imaging system. Measured results are then compared with predictive calculations based on a weighted Fresnel relation.