Particle analysis by low power He-Ne laser




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This is an extension of previous experimental research on small particle identification and counting by diffracted light measurements as performed in the Coherent Optical Laboratory at the University of Houston by Carl Dodge, under the guidance of Dr. W.L. Anderson. By using a high power argon ion laser (700 mw at wavelength 514 nm.) the proportions of two types of small plastic spheres—one type having 2 microns diameter and the other type consisting of a mixture of from k to 7 microns diameter—were estimated with good accuracy for a large range of mixtures of the two types. The purpose of the work reported in this thesis was to redesign the optical system for operation using a low power (3-k mw) He-Ne laser (at 633 nm wavelength), and to test it using the same kinds of samples as had been used by Dodge. This work has been completed and estimates obtained for percentages of the two particle types in the various mixtures. Both digital and optical analog inversion were employed, as before. All estimates fell within 2.7% of the nominal percentages. Although these are slightly poorer than the results obtained by Dodge, the conditions of the experiment essentially guarantee much improvement in accuracy by some fairly straight-forward measures. For this reason it is contended that this work shows the feasibility of the method with relatively low-level, inexpensively generated coherent light illumination.