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A Narrow Pass, Infrared Filter

IP.com Disclosure Number: IPCOM000092579D
Original Publication Date: 1966-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Welber, B: AUTHOR [+2]

Abstract

This method is for constructing narrow-pass, infrared filters with solids having a Restrahlen region. The method is based upon the scattering of electromagnetic radiation by small particles having an index of refraction n. The particles are imbedded in a carrier or host medium having an index of refraction n. The imbedded particles cause all radiation except that confined to a narrow range of delta f(1) about f(1) frequency to be scattered in the host medium. Such frequency delta f(1) is transmitted through the host medium.

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A Narrow Pass, Infrared Filter

This method is for constructing narrow-pass, infrared filters with solids having a Restrahlen region. The method is based upon the scattering of electromagnetic radiation by small particles having an index of refraction n. The particles are imbedded in a carrier or host medium having an index of refraction
n. The imbedded particles cause all radiation except that confined to a narrow range of delta f(1) about f(1) frequency to be scattered in the host medium. Such frequency delta f(1) is transmitted through the host medium.

A narrow-pass, infrared filter is constructed by crushing KBr and LiNbO(3) into powder form. Five units of KBr by weight are added to one unit of LiNbO(3). The mixture is pressed into a flat disk of about 1.3 cm. diameter by compressing the mixture in a die at 2000 psi. The resulting filter transmits a 9 micron and has a bandwidth of about 0.5 micron. See curve 1 of drawing A. The action of the filter is based on the fact that KBr has an index of refraction different from LiNbO(3) over all wavelengths except near 9 micron. Curves 2 and 3, respectively, show infrared transmission of LiNbO(3) particles imbedded in KC1 and KI. The frequencies for the latter are shifted to lower wavelengths as predicted by the above theory because KC1 and KI have each a higher index of refraction than KBr.

Curve B illustrates infrared transmission versus wavelength of MgO particles imbedded in various alkali-halide matrices. As in th...