Univ. Prof. Dr. Bernhard LENDL, Vibrational Spectroscopy at TU Vienna / Head of the CAVS Research Group, Austria

"Advances in mid-IR laser spectroscopy: New measurement modalities and applications"

Mid-infrared (Mid-IR) quantum cascade lasers stand out as coherent and polarized sources, offering rapid intensity and wavelength modulation capabilities. These features enable the development of advanced sensing strategies that extend beyond traditional absorption spectroscopy, which relies on the Beer-Lambert law.

When interacting with gaseous or liquid samples, laser radiation does more than attenuate light intensity; it also induces a phase shift in the transmitted light and heats the sample containing the analyte. While direct absorption spectroscopy primarily exploits intensity attenuation, these additional effects form the basis for dispersion spectroscopy and indirect methods like photoacoustic and photothermal spectroscopies.

This presentation will review potential measurement modalities, highlight recent instrumental advancements, and showcase selected applications. For liquid sensing, we employ broadly tunable external cavity quantum cascade lasers. We demonstrate their use in measuring protein secondary structures in water, exemplified by in-line detection in liquid chromatography and protein melting experiments. Dispersion spectroscopy will be introduced through measuring ethanol in water, illustrating its suitability for dynamic reaction monitoring. Finally recent developments in photothermal spectroscopy for trace gas sensing and near-field IR imaging will be introduced as well.