Abstract: Two arrangements are disclosed to provide high resolution measurement of sub-micrometer and micrometer particle size distributions. In a first arrangement, scattered light is measured over a wide range of scattering angles. At the same time, light scattered at low scattering angles is measured with high angular resolution. In the second arrangment, an improved Polarization Intensity Differential Scattering (PIDS) measurement is made possible by providing an interrogating light beam of selected wavelength including a first component having a linear polarization plane and a second component having a differential linear polarization plane, wherein the linear polarizations of the components are orthogonal. Photodetecting arrays in one or more scattering planes detect light scattered by the particles at least at two scattering angles.

Abstract: Methods and apparatus for measuring the intensity of light scattered by particles suspended in a sample volume illuminated by an interrogating light beam directed along an input axis, utilizing plural Fourier optical systems having lenses arranged for illuminating multiple photodetectors. The lenses of each Fourier optical system can be of different optical powers, for providing low power and high power optical trains. A low power optical train provides high resolution measurements of light scattered within a small angular range at low angles relative to the input axis, while a high power optical train provides lower resolution measurements of light scattered within a larger angular range at higher angles.

Abstract: Two arrangements are disclosed to provide high resolution measurement of sub-micrometer and micrometer particle size distributions. In a first arrangement, scattered light is measured over a wide range of scattering angles. At the same time, light scattered at low scattering angles is measured with high angular resolution. In the second arrangement an improved Polarization Intensity Differential Scattering (PIDS) measurement is made possible by providing an interrogating light beam of selected wavelength including a first component parallel to the scattering plane and a second component perpendicular to the scattering plane. Photodetecting arrangements detect light scattered by the particles at least at two scattering angles.

Abstract: An antifouling window assembly in a duct gas monitoring system comprises a mixing chamber positioned between a duct opening and a window unit. Purge gas is introduced into the mixing chamber through an inlet located adjacent the window unit. The velocity of the purge gas is such that laminar flow is established along the surface of the window unit. The purge gas circulates within the chamber and passes into the duct through the duct opening to mix with duct gases and deflect the gases from the mixing chamber.