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B. Lendl, A. Schwaighofer, G. Ramer, S. Freitag, C. Akhgar, M. Baer, B. Schmauss:
"Advancing Liquid Phase Spectroscopy by Quantum Cascade Lasers & Balanced Detection";
Vortrag: SciX 2020, online (eingeladen); 12.10.2020 - 15.10.2020.

Two new experimental set-ups for liquid phase spectroscopy will be presented, both taking advantage of unique features of QCL sources (spectral power density and inherent polarization) and a recently introduced balanced TE-cooled MCT detector. Using this detector and an EC-QCL source a dual beam set-up for transmission spectroscopy is presented and used for measuring aqueous (H2O) protein solutions. The S/N-ratio was significantly improved, allowing to record high quality protein spectra (amide I and amide II bands optical path 25 μm) enabling secondary structure analysis of the samples at concentrations of 0.1mg/mL. The second set-up introduces polarimetric ATR spectroscopy and exploits the fact that QCLs emit linear polarized light. The beam is sent into a 6 bounce trapezoidal ZnS ATR element so that the polarization plane of the beam is inclined at 45° with respect to the surface of the ATR element. After probing the sample, the exiting beam is divided in two beams by means of a ZnSe prism placed at the Brewster angle into the optical path. The exiting beam is thus divided into a beam one only containing p-polarized light, whereas the other contains s- and p-polarized light. As the effective depth of penetration (de) is different for p- and s-polarized light, absorbance values can be calculated from the two beams. In doing so the long-term stability of the set-up is improved and pulse to pulse intensity fluctuations of the laser compensated. First data on EtOH in water are shown.