A technique is described in which small (25-µm) hypervelocity (10-km/sec) in-flight particles can be detected in the presence of high background noise. The system is based on a spatial filtering principle whereby spurious noise effects are reduced by use of a eam stop in the entrance aperture of the system and a bandpass filter in the transform plane. A theoretical analysis of the system is presented, and some experimental results are obtained by detecting in-flight hypervelocity particles generated by an exploding lithium wire electrothermal accelerator.
D. M. Robinson, W. P. Chu, and J. H. Goad, "In-Flight Detection of Small Hypervelocity Particles," Appl. Opt. 12, 1524-1529 (1973)