Apparatus and method for the analysis of particle characteristics using monotonically scattered light

A method of analysing individual particle characteristics from an aerosol or other suspension of particles includes the steps of:

• directing a particle stream of finite thickness containing said particles through a scattering chamber;
• the scattering chamber including an optical system having an ellipsoidal reflector having a main focus and a secondary focus and with an orifice therein leading to a rear chamber;
• a monochromatic light source adapted to transmit a collimated beam of light along a main axis of the reflector;
• means for directing the particle stream through the beam of light at substantially the main focus of the reflector;
• collecting by means of an optical system scattered light from a solid angle of at least 3.pi. around a region where the particle stream crosses the light beam;
• the scattering chamber is associated with a detector having a two dimensional array of a multitude of sensors arranged to form an image from light scattered from a particle in the particle stream and collected by the optical system;
• recording said image in said detector and passing information to a data processor, the data processor being adapted to compare parameters of the image with parameters stored in a memory to determine the nature of the particle;
• the detector is associated with an imaging screen positioned behind the secondary focus of the reflector wherein the directing step includes locating said scattering chamber relative to said imaging screen such that, whatever part of the finite thickness of the particle stream occupied by the particle when it passes through the beam of light, rays of light scattered from the particle and imaged thereon by the optical system are monotonically ordered with respect to the angle of scattering of the rays from the particle so that the image recorded on the imaging screen is substantially independent of position of the particle in the particle stream.