title: Spatial filtering technique to image and measure two-dimensional near-forward scattering from single particles.
abstract: This work describes the design and use of an optical apparatus to measure the far-field elastic light-scattering pattern for a single particle over two angular-dimensions. A spatial filter composed of a mirror with a small through-hole is used to enable collection of the pattern uncommonly close to the forward direction; to within tenths of a degree. Minor modifications of the design allow for the simultaneous measurement of a particle's image along with its two-dimensional scattering pattern. Example measurements are presented involving single micrometer-sized glass spherical particles confined in an electrodynamic trap and a dilute suspension of polystyrene latex particles in water. A small forward-angle technique, called Guinier analysis, is used to determine a particle-size estimate directly from the measured pattern without a priori knowledge of the particle refractive index. Comparison of these size estimates to those obtained by fitting the measurements to Mie theory reveals relative errors low as 2%.
authors.affiliation: US Army Research Laboratory, RDRL-CIE-S, 2800 Powder Mill Road, Adelphi, MD 20783-1197, USA. mberg81@gmail.com
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Berg
authors.forename: Steven C
authors.initials: SC
authors.lastname: Hill
authors.forename: Gorden
authors.initials: G
authors.lastname: Videen
authors.forename: Kristan P
authors.initials: KP
authors.lastname: Gurton