15 October 2004 The measurement system for evaluating the relation between adsorption quantity of gaseous contaminants and optical transmissivity degradation
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Abstract
Gaseous contamination on an optical surface causes a degradation of the transmissivity and reflectivity of an optical surface, an increase light scattering and a deterioration of optical characteristics.In optical sensors installed in earth observation satellites, the extraction of physical quantities must be reliable, and deterioration of the optical system due to gas adsorption is a leading factor which reduces the reliability of sensor output data derived from acquired data.We developed a measurement system to quantitatively evaluate the transmissivity decrease of optical surfaces due to gas adsorption in the visible and near- infrared regions where the optical sensors used for earth observation have many observation bands.In this system, a gas having known components was adsorbed on a glass material installed in a container under vacuum, and the spectral transmittance before and after adsorption was measured. The gas adsorption amount on the sample glass material was controlled by controlling the gas injection pressure and sample surface temperature.The gas injection pressure can be controlled from atmospheric pressure to 4x10-4Pa, and the temperature can be controlled from -140°C to +125°C to a precision of 0.02K. As this instrument can control the injection pressure of the adsorption gas and the sample glass material temperature when installed in the measurement optical path, the transmissivity can be measured while continually varying the gas pressure and sample temperature. The transmissivity change due to gas adsorption can be measured within a wavelength range of 250 to 2500nm to a precision of 0.15%.
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Nobunari Itoh, "The measurement system for evaluating the relation between adsorption quantity of gaseous contaminants and optical transmissivity degradation", Proc. SPIE 5526, Optical Systems Degradation, Contamination, and Stray Light: Effects, Measurements, and Control, (15 October 2004); doi: 10.1117/12.559252; https://doi.org/10.1117/12.559252
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KEYWORDS
Adsorption

Glasses

Temperature metrology

Protactinium

Spectrophotometry

Sensors

Optical testing

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