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.

Using a supercontinuum laser, reflective optics, and a spatial filter, we measure two-dimensional small-angle light-scattering patterns for a variety of microparticles including spheres, salt, sand, and volcanic dust. The measurements are done at 13 wavelengths from 450–850 nm, where the absence of refractive optical elements minimizes the effects of chromatic aberration. Qualitative particle-material sensitivity is demonstrated by layering differently colored patterns. Last, the multispectral capability of our device demonstrates a new possibility to probe different q -space regimes for a given particle in a single measurement.

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