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Browse Prior Art Database

Interference Fringes for the Detection of Airborne Particles

IP.com Disclosure Number: IPCOM000043668D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Goodman, DS: AUTHOR [+3]

Abstract

An airborne particle detector is described in which the air is passed through a spatially non-uniformly illuminated region (such as an interference fringe field) and scattered light is detected. Improved sensitivity and S/N ratio are possible by properly matching the characteristics of the detection scheme to the characteristics of the non-uniform illumination. Low-defect production of microelectronics requires an environment that is virtually free of particulate contaminants. There is a great need for a good method of detecting and measuring this type of contamination. We describe here a new class of instruments for the detection of airborne particles. In these devices (Fig. 1) the stream of air to be tested passes through an illuminated region having an irradiance which varies with position in some prescribed way.

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Interference Fringes for the Detection of Airborne Particles

An airborne particle detector is described in which the air is passed through a spatially non-uniformly illuminated region (such as an interference fringe field) and scattered light is detected. Improved sensitivity and S/N ratio are possible by properly matching the characteristics of the detection scheme to the characteristics of the non-uniform illumination. Low-defect production of microelectronics requires an environment that is virtually free of particulate contaminants. There is a great need for a good method of detecting and measuring this type of contamination. We describe here a new class of instruments for the detection of airborne particles. In these devices (Fig. 1) the stream of air to be tested passes through an illuminated region having an irradiance which varies with position in some prescribed way. The light scattered from a particle as it passes through this region, therefore, is modulated. This modulated light is then sensed by a detector having supporting electronics designed especially for the particular signal that is produced. The combination of light intensity distribution and electronics can be chosen to improve particle detection sensitivity or to measure particle size. One such device is shown in Fig.
2. Here a simple interference pattern of straight fringes is produced from a collimated laser beam. The air flow is perpendicular to the fringes. As a particle traverses the fri...