Evaluation of Optical Arrangements for Ballistic Imaging in Sprays

This work investigates the imaging performance, in terms of
contrast and resolution, of two different time-gated ballistic imaging setups
commonly used in spray research. It is shown that the two setups generate
similar spatial resolution in the presence of scattering media. The simpler
(2f ) setup, however, was less sensitive to component misalignments
and time-gate induced aberrations than the commonly used (4f ) system.
Measurements comparing both arrangements indicated slightly higher contrast
for the 2f system under the densest conditions for small scatterers. Subsequent
computational modeling confirmed the observed tolerance of the 2f
system to misalignment and gate effects.
The best performing setup was also compared experimentally to its nontime-
gated shadow-imaging equivalent, to establish when the time-gate
enhances imaging performance. It is shown that the time-gated setup
generates higher contrast under almost all of the scattering conditions
tested, while the non-time-gated setup generates higher spatial resolution
only in the lower scatterer size range at the lowest scatterer concentrations.