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Emission Spectrophotometer

IP.com Disclosure Number: IPCOM000085929D
Original Publication Date: 1976-Jun-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Mueller, KA: AUTHOR [+2]

Abstract

The infrared (or visible) absorptance of low-loss optical materials can be measured by investigating their corresponding emittance (Kirchhoffs law). In an emission spectrophotometer the test sample is attached to a permanently installed crystal. It is heated by thermal conduction and partially by the radiation from this crystal. Thermal conduction is caused by phonons in the crystal and the sample, the spectra of which overlap in any case. Heat transfer by radiation will take place at frequencies where the absorption spectra of the crystal and the sample overlap.

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Emission Spectrophotometer

The infrared (or visible) absorptance of low-loss optical materials can be measured by investigating their corresponding emittance (Kirchhoffs law). In an emission spectrophotometer the test sample is attached to a permanently installed crystal. It is heated by thermal conduction and partially by the radiation from this crystal. Thermal conduction is caused by phonons in the crystal and the sample, the spectra of which overlap in any case. Heat transfer by radiation will take place at frequencies where the absorption spectra of the crystal and the sample overlap.

That crystal is the target of a suitably adapted laser beam. Crystal and laser are chosen such that the crystal shows no absorption or only very low absorption (and emission) in the range where the instrument is to be used, like in the infrared. (See range I.R. in the insert of the drawing.) But it has a (narrow or wide) absorption band at an appropriate laser frequency Nu -LASER. This transition must decay, at least partially, radiationless. Due to the very low emissivity of the permanent crystal in the frequency range of interest, the disturbing stray-light emission can be kept at an extremely low level in the order of 10/-4/ through 10/-7/.

The sample will raise its temperature until the thermally emitted energy equals the absorbed energy. The laser radiation is first chopped at a frequency relatively small compared with the thermal relaxation rate of the sample. Contributio...