Synchronous interferometric probing of microscopic and nanoscale materials

Abstract

A new method for the rapid detection and tracking of individual microscopic and nanoscale particles is demonstrated, based on inexpensive, low-power, diode-laser light sources and photodiode receivers. Using a swept standing-wave laser probe and a phase-sensitive detector, single micrometer-sized particles are simply and easily monitored via the scattered light in the far-field. Also, strong signals are obtained in the forward-scattering direction via the resulting modulation of the transmitted probe beam power. We report on our verification and testing of the method via detailed measurements and theoretical modeling of signals from mounted and oriented microfibers. Also, we give results of particle sizing measurements for distributions of metallic and nonmetallic micro-particles, with comparative sizing obtained from optical and electron microscopy. Further, we discuss and demonstrate extensions of this technique to a novel and highly sensitive form of optical phase-contrast imaging.