Review of the Fraunhofer diffraction particle-sizing technique

The Fraunhofer diffraction technique for measuring particle size distributions was originally developed for the measurement of spray drop-size distributions at the University of Sheffield in 1976. It has since become an industry standard for the optical characterization of sprays. In this paper, the basic theory is described and further developments of the technique are discussed. These developments include: the use of calibration standards, such as standard reference materials and photomask reticles; the limits to spray concentration imposed by multiple scattering and the theoretical analysis of multiple scattering; the limitations to the physical scale of a spray plume caused by vignetting by the collection lens system; and the tomographic transformation of 'line-of-sight' data to give radial profiles of drop-size distributions. Comparisons made between laser diffraction data and other techniques such as flash photography and laser Doppler velocimeter (LDV)-based instruments are also discussed.