Laser retroreflectance consistent with a polarized single-scatter weak electromagnetic-field
Abstract:
A set of laser retroreflectance measurements at 0.6328 and 1.159 pum are presented for white and red Nextel paints, MgCO(3), and Halon for phase angles from 12.1° to 0°, with incident radiation perpendicular and parallel to the plane of vision, to determine plane- and cross-polarized components. It is shown that a physical optical retroreflectance can occur for a polarized single-asperity surface scatter or selected multiple scattering that preserves the source polarization and coherence. Also subsequent geometrical optical shadowing of the scattering can occur. At very high resolutions (˜0.1°), an optical structure appears on the retroreflectance patterns suggesting a physical optical interference. The observations support a theory of retroreflectance based on weak electromagnetic-field localization, and extend these concepts with observations of unpolarized scattering. Ideally the dominant, sharp retroreflectance peak is theoretically predicted to be twice the diffuse-background level, and this has been observed for some samples. At higher angular and spectral resolutions, retroreflectance thus appears to be a combination of physical and geometrical optical effects.
