The optical extinction caused by a small particle, such as an aerosol
particle, is an important measurable quantity. Understanding the
influence of atmospheric aerosols on the climate, assessing visibility
in urban environments, and remote sensing applications such as lidar
all need accurate measurements
of particle extinction. While multiple methods are known to measure
extinction, digital in-line holography (DIH) features the unique
ability to provide contact-free images of particles simultaneously
with estimates for the extinction cross section. This is achieved
through an integration of a measured hologram followed by an
extrapolation. By means of a supercontinuum laser, we investigate the
measurement of the cross section via DIH for stationary particles
across a broad spectrum, from 440 nm to 1040 nm. The
particles considered include a 50 µm glass microsphere, a
volcanic ash particle, and an iron(III) oxide particle. The results
show the ability to estimate a particle’s cross section to within 10%
error across portions of the spectrum and approximately 20% error
otherwise. An examination of the accompanying hologram-derived
particle images reveals details in the images that evolve with
wavelength. The behavior suggests a basic means to resolve whether
absorption or scattering dominates a particle’s extinction.