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A. Dabrowska, M. David, A. Schwaighofer, S. Freitag, A. M. Andrews, G. Strasser, B. Hinkov, B. Lendl:
"Broadband Mid-Infrared Spectroscopy employing a Quantum Cascade Laser and a Quantum Cascade Detector for Milk Protein Analysis";
Poster: SCIX 2021, Providence, Rhode Island, USA; 26.09.2021 - 01.10.2021.

In laser-based mid-infrared (mid-IR) spectroscopy mainly mercury cadmium telluride (MCT) detectors are used. Unfortunately, these detectors suffer from a rather narrow linear range. This is especially problematic when analyzing aqueous samples covering the broad amide I and amide II region, because of strongly varying water background absorption in that region. Therefore, when using MCTs additional elements have to be added to the optical path to stay within the linear range of the MCTs. Mainly attenuation of radiation in the amide II range is needed, thus significantly reducing the power advantage of mid-IR laser spectroscopy. [1] 
With the achieved progress in quantum engineering technologies, a new type of detector has emerged as better-suited candidate. Quantum cascade detectors (QCDs) offer room-temperature operation, fast response time, low noise, and high potential for integration. In contrast to MCTs, QCDs operate in a wide power range of the incident radiation without saturation effects while maintaining excellent linearity.
In this work, we combine a widely tunable EC-QCL (>260 cm-1) with a spectrally tailored in-house developed QCD to record spectra of aqueous bovine milk protein samples. Obtained S/N-ratio and recorded spectra are compared with those recorded on FTIR spectrometers employing MCTs as well as pyroelectric detectors.

quantum cascade detector, quantum cascade laser, mid-infrared spectroscopy, physical chemosensors, milk protein analysis