Optical submicron particle detector

PURPOSE: To detect a submicron particle in a closed region without requiring a precise optical alignment by focusing the starting points of two diverging beams in a closed inspection region while crossing each other and analyzing an electric signal generated from a particle passing through the crossing region. CONSTITUTION: A polarized beam from a laser 10 is focused through a lens 12 onto a black cell 14 and when a signal is applied from a local oscillator 15, a beam 16 is generated in addition to a beam 18 and the optical frequency of the beam 16 is modulated. The beams 16, 18 are passed through a lens 20 and a window 26 and focused in a closed region 22 and when the starting point of the beam 16 is focused in the cell 14, the beams 16, 18 cross at a known point to generate a moving pattern. When a particle 24 enters into the cross region, a burst subjected to Doppler shift by the optical frequency of the beam 18 is induced and an electric signal is generated. The beam 16 passed through a window 28 is absorbed by a damp 30 and the beam 18 is directed to a photocell 32. Output from the photocell 32 is delivered to a signal processor 34 and the particle 24 is detected. COPYRIGHT: (C)1993,JPO