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Improving Optical Transmission Measurements in Powdered Layer Samples with Pinholes

IP.com Disclosure Number: IPCOM000079983D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Taub, HH: AUTHOR

Abstract

It is often necessary to measure the transmission (i.e., attenuation) of light in powdered layer samples, such as in the case of cathodochromic materials settled or sprayed onto a glass or mica substrate, where it is desired to measure the transmission contrast ratio between darkened and undarkened regions. One difficulty that frequently arises with this measurement, is that the powdered layer has pinholes over as much as 0.1% of the area being measured. Since the light transmitted through the material is often attenuated by a factor of 1000, the light passing directly through the pinholes can contribute as much to the detected light intensity as the light attenuated through the powder. This greatly reduces the accuracy of the measurement.

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Improving Optical Transmission Measurements in Powdered Layer Samples with Pinholes

It is often necessary to measure the transmission (i.e., attenuation) of light in powdered layer samples, such as in the case of cathodochromic materials settled or sprayed onto a glass or mica substrate, where it is desired to measure the transmission contrast ratio between darkened and undarkened regions. One difficulty that frequently arises with this measurement, is that the powdered layer has pinholes over as much as 0.1% of the area being measured. Since the light transmitted through the material is often attenuated by a factor of 1000, the light passing directly through the pinholes can contribute as much to the detected light intensity as the light attenuated through the powder. This greatly reduces the accuracy of the measurement.

To eliminate this problem, two crossed polarizers may be employed as illustrated. With the polarizer and analyzer crossed, the intensity detected at the photo-spotmeter due to the light passing through the pinholes can be made arbitrarily small with high-quality polarizers. The light transmitted through the powder, however, becomes largely unpolarized and consequently it is easy to detect a signal from this area. The overall transmitted intensity is decreased due to the polarizers, but this may be readily compensated for by increasing the intensity of the light source. With the arrangement shown, the pinholes appear to vanish completely and the...