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T. Vahlsing, H. Moser, M. Grafen, K. Nalpantidis, M. Brandstetter, H. Heise, B. Lendl, S. Leonhardt, D. Ihrig, A. Ostendorf:
"Mid-infrared spectroscopic characterisation of an ultra-broadband tunable EC-QCL system intended for biomedical applications";
in: "Clinical and Biomedical Spectroscopy and Imaging IV", herausgegeben von: SPIE; Proc. SPIE, 2015, S. 953713-1 - 953713-12.

Mid-infrared spectroscopy has been successfully applied for reagent-free clinical chemistry applications. Our aim is to
design a portable bed-side system for ICU patient monitoring, based on mid-infrared absorption spectra of continuously
sampled body-fluids. Robust and miniature bed-side systems can be achieved with tunable external cavity quantum
cascade lasers (EC-QCL). Previously, single EC-QCL modules covering a wavenumber interval up to 250 cm-1 have
been utilized. However, for broader applicability in biomedical research an extended interval around the mid-infrared
fingerprint region should be accessible, which is possible with at least three or four EC-QCL modules. For such purpose,
a tunable ultra-broadband system (1920 - 780 cm-1, Block Engineering) has been studied with regard to its transient
emission characteristics in ns time resolution during different laser pulse widths using a VERTEX 80v FTIR
spectrometer with step-scan option. Furthermore, laser emission line profiles of all four incorporated EC-QCL modules
have been analysed at high spectral resolution (0.08 cm-1) and beam profiles with few deviations from the TEM 00
spatial mode have been manifested. Emission line reproducibility has been tested for various wavenumbers in step tune
mode. The overall accuracy of manufacturer default wavenumber setting has been found between ± 3 cm-1 compared to
the FTIR spectrometer scale. With regard to an application in clinical chemistry, theoretically achievable concentration
accuracies for different blood substrates based on blood plasma and dialysate spectra previously recorded by FTIRspectrometers
have been estimated taking into account the now accessible extended wavenumber interval.

Infrared spectroscopy, quantum cascade lasers with external cavity, ultrabroadband application, ns-time resolved spectroscopy, pulse characterisation, emission laser mode characterisation

http://dx.doi.org/10.1117/12.2183952