Two-dimensional small-angle scattering from single particles in infrared with a lensless technique

Opt Express. 2020 Aug 17;28(17):25114-25122. doi: 10.1364/OE.397699.

Abstract

An experiment is described where two-dimensional small-angle light scattering (2D-SALS) patterns from single particles are measured in the infrared through a lens-free approach. Spatial filtering is employed to separate scattered light from unscattered light to within approximately one degree from the forward direction. Non-planar reflective elements are used in the filtering process, permitting 2D-SALS measurements to be done without chromatic aberrations over a broad spectral range and from 0.8 to 8 degrees in the polar scattering angle and zero to 360 degrees in the azimuthal angle. Patterns from spherical microparticles are presented along with nonspherical particles including volcanic ash and salt. An asymmetry analysis is applied to demonstrate an ability to differentiate spherical from nonspherical particles from the 2D-SALS patterns.