Detection of small particles in fluid flow using a self-mixing laser

Abstract

We describe a highly sensitive, real-time method of detecting small particles in a fluid flow by self-mixing laser Doppler measurement with a laser-diode-pumped, thin-slice solid-state laser with extremely high optical sensitivity. Asymmetric power spectra of the laser output modulated by the re-injected scattered light from the small particles moving in a dilute sample-flow, through a small-diameter glass pipe, were observed. The observed power spectra are shown to reflect the velocity distribution of the fluid flow, which obeys Poiseuille's law. Quick measurements of flow rate and kinetic viscosities of water-glycerol mixtures were also performed successfully. Measurable low-concentration limits for 262-nm polystyrene latex spheres and 3-mum red blood cells in a fluid flow were below 1 and 10 ppm, respectively, in the present self-mixing laser Doppler velocimeter system.

Analysis of molecular dynamics of colloidal particles in transported dilute samples by self-mixing laser Doppler velocimetry

“…In this case, the power spectrum of the modulated wave induced by the Brownian motion of the particles becomes Lorentzian. On the other hand, we also demonstrated that self-mixing LDV is applicable to velocimetry of the fluid flow containing nanosize tracer particles through a glass pipe [6,7]. In this case, the power spectrum has a complex line shape because the velocity distribution of the particles in the pipe obeys Poiseuille's law.…”

“…Thus, the velocity of the target can be obtained from the observation of the intensity-modulated laser light. We have developed several self-mixing LDV systems with thin-slice solid-state lasers, such as a selfmixing particle analyzer [5,6] and a flowmeter [6,7]. Solid-state lasers with highly doped active ions having an extremely short absorption length for laser-diode pumping are suitable for thin-slice cavity configurations, and these lasers result in an extremely short photon lifetime compared with fluorescence lifetimes.…”

Self-Mixing Thin-Slice Solid-State Laser Metrology

“…Here, the fitting procedure is as follows: Thirty Gaussian functions are set within the observed power spectrum, whose center frequencies f Di are equally spaced, to describe the velocity distributions. v i -values are derived using Equation (14) and w i -values are determined using the empirical relation, w i = 574,100 v i , which was experimentally obtained from the Gaussian curve fitting of time dependent power spectra for 262-nm-diameter PS particles in ‘dropped water’ from the vertical pipe shown in Figure 15 [40]. Here, the velocity distribution of the PS particles in the light path is very small, i.e.…”

“…v i -values are derived using Equation (14) and w i -values are determined using the empirical relation, w i = 574,100 v i , which was experimentally obtained from the Gaussian curve fitting of time dependent power spectra for 262-nm-diameter PS particles in ‘dropped water’ from the vertical pipe shown in Figure 15 [40]. Here, the velocity distribution of the PS particles in the light path is very small, i.e.…”

“…Configuration of the flow passage for a dilute sample-flow (reprinted with permission from [40]; © Copyright 2007, Optical Society of America).…”