HOLOGRAM TECHNIQUES FOR PARTICLE‐SIZE ANALYSIS

Abstract

SummaryFraunhofer hologram camera systems have been applied to a number of applications for particle‐size analysis. Reconstructed holograms provide high‐quality images with three orders of magnitude greater depth of field than that provided by a microscope. Instantaneous recording of dynamic dispersions with freedom from isokinetric sampling losses is one of the chief attractions of the method. A permanent record of the particle distribution that can easily be recalled is produced. The typical laser pulse length of 20 nanoseconds allows particles to be moving at high velocities; the maximum particle velocity criterion is that the particle shall move less than 1/10 diameter during the exposure time.A hologram has extremely high information content; in fact, it contains the size, shape and position in three‐dimensional space of a large number of objects. The price that must be paid for recording this large amount of information is that lasers and precision optical systems must be used in a two‐step process to record and reconstruct the holograms.Hologram photography has, however, all the advantages of direct photography; it gives shape information and shows the minute detail of the microcosm. Scientists trained to utilize this new hologram technique can further their work in fine‐particle analysis.