PARTICLES DETECTING DEVICE USING LIGHT

PURPOSE:To catch scattered light without converging it on one point through an optical system by giving a light irradiating means two long and short focuses, and positioning a particle array at the short focus and providing a partial light shield member and a stray light removing member. CONSTITUTION:A light beam (a) from a light source is passed through a columnar concave lens 8 and a convex lens 9 to form the short focus F1 and long focus F2, and the luminous flux is cut off in a semielliptic shape by the partial light shield member 7 between both focuses F1 and F2. The short focus F1 is positioned in the center of a flow cell 2 and the light beam (a) strikes on the particle array 1 in the flow cell 2 to generate scattered light. Straight traveling light (c) and marginal stray light are cut off by the stray light removing member 5 and only the scattered light passes through the light passing hole 6 of the stray light removing member 5 and is detected by a light receiver 4. At this time, light on one side of an optical axis A is cut off by the partial light shield member 7, so the light passing hole 6 of the stray light removing member 5 is put closer to the optical axis A to catch scattered light close to the optical axis A.