L.E.
McNeil, R.H. French, “Light Scattering From Red Pigment Particles: Multiple Scattering in a Strongly Absorbing System”, Journal
of Applied Physics, 89, 1, 283-93, (2001).
L.E. McNeil,
A.R. Hanuska, R. H. French, “Near-field scattering from
red pigment particles: absorption
and spectral dependence”,Journal
of Applied Physics, 89, 1, 283-93, (2001).
Near-field scattering from red pigment particles:
absorption and spectral dependence
L.E. McNeil*
Dept.
of Physics and Astronomy, Univ. of North Carolina at Chapel Hill, Chapel Hill,
NC 27599-3255
A.R.
Hanuska and R.H. French
DuPont
Central Research and Development, Wilmington, DE 19880-0356
When film coatings are made of pigment particles embedded in a transparent
resin, the optical characteristics of the resulting film are determined not only
by the bulk optical properties of the constituent materials, but also by the
spatial distribution of the light scattered from small particles. If the
particles are separated by distances comparable to their diameter, as is the
case for high particle concentrations or agglomerated systems, the near-field
interactions between the radiation fields of the particles can strongly
influence the resulting far-field intensity distribution. In this work we
have used full-field finite-element solutions of Maxwell’s equations to
calculate the near- and far-field scattering patterns for single 500‑nm
quinacridone spheres and for pairs of particles. We find that the
scattered intensity forms a forward-directed plume that extends far beyond the
particle surface, especially at short wavelengths and where the absorption is
large. This results in near-field interactions between pairs of particles
that can either increase or decrease the scattering (both the total scattering
and the fraction of the scattered light that is directed into the backward
hemisphere), depending on the orientation of the particle pair relative to the
direction of the incident light. In some cases, particularly if the
particles are aligned along the incident direction, the two spheres can produce
a far-field scattering distribution that is approximately that of a single,
larger (sometimes much larger) sphere. If the particles are aligned
perpendicular to the incident direction, the strength of the scattering per
particle volume is roughly the same as for a single particle, but the scattering
is more forward-directed. These interaction effects occur even though the
surface-to-surface separation of the particles is larger than the distance for
which a single particle shows significant scattered intensity. These
near-field and far-field phenomena are beyond the limitations of
single-scattering and independent multiple-scattering approaches, and the
near-field interactions can have a significant effect on the scattering of light
from films containing such particles, especially if they tend to form oriented
clusters.
Figure 1: Scattered intensity for absorbing particles in absorbing
resin. All intensity scales in
units of incident intensity. (a)
Single particle, l = 270 nm. Spatial scale 1 mm x
2 mm, intensity scale 2.17 (red) –
2.32 x 10-3 (blue). (b)
Two particles in the side-by-side configuration, l = 270 nm.
Spatial scale 2 mm x 2 mm,
intensity scale 2.22 (red) – 1.83 x 10-3 (blue). (c) Two particles in the in-line configuration, l = 270 nm. Spatial scale 1 mm x 5 mm, intensity
scale 1.81 (red) – 2.20 x 10-3 (blue) (d) Single particle, l = 390 nm. Spatial scale 1 mm
x 2 mm, intensity scale 23.4 (red) –
4.59 x 10-3 (blue). (e)
Two particles in the side-by-side configuration, l = 390 nm. Spatial scale 2 mm x 2 mm, intensity
scale 22.8 (red) – 5.97 x 10-3 (blue). (f) Two particles in the in-line configuration, l = 390 nm. Spatial scale 1 mm
x 5 mm, intensity scale 23.4 (red) –
2.49 x 10-3 (blue).
Figure 2: Scattered intensity for absorbing particles in absorbing
resin. All intensity scales in
units of incident intensity. (a)
Single particle, l = 560 nm. Spatial scale 1 mm x 2 mm, intensity
scale 2.07 (red) – 3.90 x 10-3 (blue). (b) Two particles in the side-by-side configuration, l = 560 nm.
Spatial scale 2 mm x 2 mm,
intensity scale 1.93 (red) – 3.04 x 10-3 (blue). (c) Two particles in the in-line configuration, l = 560 nm. Spatial scale 1 mm x 5 mm, intensity
scale 2.07 (red) – 4.05 x 10-3 (blue) (d) Single particle, l = 750 nm. Spatial scale 1 mm
x 2 mm, intensity scale 10.4 (red) –
4.76 x 10-3 (blue). (e)
Two particles in the side-by-side configuration, l = 750 nm. Spatial scale 2 mm x 2 mm, intensity
scale 10.2 (red) – 2.75 x 10-3 (blue). (f) Two particles in the in-line configuration, l = 750 nm. Spatial scale 1 mm
x 5 mm, intensity scale 16.5 (red) –
4.37 x 10-3 (blue).
