Patent ID: 7399600

Claim:
A method for the optical detection and/or analysis of sub-micron particulates comprising the steps of: illuminating, with a focused beam of radiation from a source, a substrate, part of one surface of which substrate is coated with a film comprising an optically opaque metal, and part of which surface is left uncoated, such that the surface has a coated portion and an uncoated portion, the focused optical beam being incident on the substrate at a point on the uncoated portion of the surface adjacent or close to, but not coincident with, the metal film coated portion of the surface, such that at least a portion of the optical beam is caused to propagate above, but parallel or at an angle of less than 5° and close to, the surface of the metal film; placing onto the surface of the substrate a sample containing a particle or population of particles of sub-micron dimensions such that particles enter a region illuminated by the optical beam propagating above but close to the metal film; individually detecting, by a suitable lens and detector arrangement situated in the far field at normal or high angle to the plane of the metal film, the optical radiation individually scattered by, or otherwise caused to emanate from, the individual particles through their interaction with the optical beam.