Particle sizing and flow measurement using self-mixing interferometry with a laser diode

New applications are presented for self-mixing interferometry, based on optical scattering, feedback and self-mixing in laser diodes. The self-mixing interferometry method has been developed for the determination of sub-micron particle sizes and for the measurement of flows in narrow diameter tubes. The rate equations for laser diodes subjected to frequency-shifted feedback are reviewed and extended to include a normalized frequency distribution to be characterized by the backscattered light spectrum. Experimental investigations are presented for (a) particle sizing using polystyrene particles in water from 0.02 to 0.20 νm in diameter and (b) for transverse velocity profile determination using a 1.4 mm diameter tube with flow rates ranging between 10 and 100 ml h-1. The observed frequency band increases for smaller particles when observing Brownian motion and for higher flow rates when observing flowing liquids. This experimental technique is inherently simple and low cost. Further potential applications of this technique include blood flow measurement in medicine, electrophoresis investigations in biology and particle characterization in process engineering and chemistry. © 2005 IOP Publishing Ltd.