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10 January 1997 Liquid mixture detection by InGaAsP semiconductor lasers
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Compact liquid sensors were constructed by using the output of near-infrared semiconductor diode lasers to measure transmission. Multiple short external cavities were used to force diode lasers to provide a wide spectral coverage (approximately equals 72 nm) for the detection of broad absorption features of liquids. The transmission at discrete laser modes were processed by the principal component regression (PCR) and the partial least squares (PLS) algorithms. A root mean square error of prediction of 0.092% and a correlation coefficient R2 of 0.998 were obtained for the detection of water concentration in D2O. The rms value of 0.056% from 30 independent measurements of 0.5% water in D2P showed that the method was sensitive to detect 0.1% concentration difference. The application of the PCR and the PLS algorithms in the scheme was studied in a three mixture system of water, acetone and methanol in terms of optimizing factors and detection of 'outliers'. The limiting noise sources were determined by modeling synthetic data.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Xiang Zhu and Daniel T. Cassidy "Liquid mixture detection by InGaAsP semiconductor lasers", Proc. SPIE 3000, Laser Diode and LED Applications III, (10 January 1997);

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