This Small Business Innovation Research (SBIR) Phase I project will show proof of principle for an innovative optical technique using backscattered laser light to perform particle sizing measurements. Limitations of existing systems include the need to measure transmitted instead of reflected light, the inability to make accurate measurements in dense particles fields, and the inability to characterize particle shape. Phase I research will lead to the realization of a unique diagnostic system capable of fast, non-invasive measurements in media of high turbidity; use of backscattered, not transmitted, light; solid-state fiber optic construction; cost effective gain-guided laser diodes for light sources; and assembly from commercial-off-the-shelf components. Particle sizing techniques are critical for process characterization and control in diverse areas of manufacturing and research. The worldwide market for particle sizing instruments has been estimated at $300 million. Industries using particle sizing include agrochemical, cement, ceramics, cosmetics, personal care, soil testing, wastewater processing, paints, inks and other surface coatings. The proposed system will introduce a patentable new technology to the field of particle sizing by the novel extension of a proven commercial technique