31 January 2014 Measures for optimizing pulsed EC-QC laser spectroscopy of liquids and application to multi-analyte blood analysis
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Abstract
We employed a broadly tunable pulsed external cavity (EC)-QC laser with a spectral tuning range from 1030 cm-1 to 1230 cm-1 and a tuning speed of 166 cm-1/s for direct absorption spectroscopy of aqueous solutions. The laser offered spectral power densities of up to four orders of magnitude higher than available with a conventional FTIR spectrometer. Therefore, a portable demonstration system with a large optical path length transmission flow cell (165 μm) could be realized preventing clogging of the flow cell. In pulsed mode an EC-QC laser provides significantly higher peak power levels than in continuous-wave mode, but pulse-to-pulse intensity variations, intra-pulse mode hops and mechanical imperfections of the scanning mechanism significantly impair the quality of resulting absorbance spectra. This article reports on measures which we found appropriate to reduce the initially high noise level of EC-QC laser absorbance spectra. These measures include a spectral self-referencing algorithm that makes use of the inherent structure of the EC-QC laser's gain curve to correct laser instabilities, as well as Fourier filtering, among others. This enabled us to derive infrared spectra which were finally useful for quantitative analysis in blood plasma samples. Finally, with the appropriate measures in place and using partial least squares regression analysis it was possible to simultaneously quantify 6 blood analytes from a single physical measurement of a 200 μL blood sample. This proves the potential of EC-QC lasers for practical application in clinical point of care analysis.
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M. Brandstetter, M. Brandstetter, C. Koch, C. Koch, A. Genner, A. Genner, B. Lendl, B. Lendl, } "Measures for optimizing pulsed EC-QC laser spectroscopy of liquids and application to multi-analyte blood analysis", Proc. SPIE 8993, Quantum Sensing and Nanophotonic Devices XI, 89931U (31 January 2014); doi: 10.1117/12.2038585; https://doi.org/10.1117/12.2038585
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