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Particle Detection Technique

IP.com Disclosure Number: IPCOM000040804D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Batchelder, JS: AUTHOR [+2]

Abstract

Particles whose diameters are on the order of the wavelength of light can be detected by locally heating the surface of a substrate and noting directional changes in non-specular light scattering lobes with respect to time.

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Particle Detection Technique

Particles whose diameters are on the order of the wavelength of light can be detected by locally heating the surface of a substrate and noting directional changes in non-specular light scattering lobes with respect to time.

Referring to the figure, an incident, modulated pump beam 1 of one wavelength is arranged to be coincident with a steady probe beam 2 of a second wavelength at beam splitter 3 and directed through lens 4 to substrate 5. An array of detectors 6 senses reflected light. Material on substrate 5 in good thermal contact will not be appreciably affected by the pump beam because of efficient thermal dissipation. The far field scatter lobes of light from the surface remain stationary, as sensed by detectors 6.

If a particle is not in good thermal contact with substrate 5, it will heat and change shape in response to the pump beam energy. This produces a change in polar and azimuthal angles of the light scattering lobes. A transient component results in the detector output signals and indicates the poor local thermal conduction.

The structure of the scattering lobes is sensitive to shape and orientation of particles. Since particle direction is unknown, detector array is necessary. The modulated scatter component will be observed only by detectors spatially smaller than the scattering lobes.

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