Estimate of the threshold sensitivity of laser microparticle analyzers

Abstract

The particles being investigated in the analyzers, being in the suspended state in a gas or liquid medium, proceed under pressure into a flow-through chamber transparent to the laser beam. Aero- or hydrodynamic focusing [3] of the particle trajectories with respect to the center 0 of the measurement zone coincident with the greatest flux density I(x = 0, y = 0, z = 0) of the illuminating beam [4~ 5] occurs within the chamber. Therefore, the particles move in the XOY plane at a velocity V along the OX axis and intersect a continuous laser beam one after the other that is being prop~Bted along the OZ axis (OZ I XOY). In order to improve the threshold characteristics of the LA the illuminating beam is focused in the XOY plane in an elliptical beam (general case) with minor o):,(o~OX) and major ,~y semi-axes at the level exp(-2) of maximal intensity [4, 5]. As a result of the interaction of the laser beam by an individual particle, a pulse signal is formed at the photodetector output located on the LA optical axis, that is proportional to the component Pa t of the attenuated radiation flux. If the photodetector were located at a certain angle to the optical axis in such a manner that direct laser radiation would not be incident on it then the scattered component of the radiation flux Ps(t) would be recorded. It is known [4] that the radiation flux recordable by the photodetector is determined by the expression P(t,Q,p,m)~ P~aknon ,(t,p)ai(Q ,p ,m),