Abstract

Acquisition of classical absorption spectra of liquids in the mid-IR range with quantum cascade lasers (QCLs) is often limited in sensitivity by noise from the laser source. Alternatively, measurement of molecular dispersion (i.e., refractive index) spectra poses an experimental approach that is immune to intensity fluctuations and further offers a direct relationship between the recorded signal and the sample concentration. In this work, we present an external cavity quantum cascade laser (EC-QCL) based Mach–Zehnder interferometer setup to determine dispersion spectra of liquid samples. We present two approaches for acquisition of refractive index spectra and compare the qualitative experimental results. Furthermore, the performance for quantitative analysis is evaluated. Finally, multivariate analysis of a spectrally complex mixture comprising three different sugars is performed. The obtained figures of merit by partial least squares (PLS) regression modelling compare well with standard absorption spectroscopy, demonstrating the potential of the introduced dispersion spectroscopic method for quantitative chemical analysis.

© 2020 The Author(s)

Mid-IR refractive index sensor for detecting proteins employing an external cavity quantum cascade laser-based Mach-Zehnder interferometer

Alicja Dabrowska, Andreas Schwaighofer, Stefan Lindner, and Bernhard Lendl
Opt. Express 28(24) 36632-36642 (2020)

Mid-infrared photoacoustic spectroscopy of solids using an external-cavity quantum-cascade laser

Qing Wen and Kirk H. Michaelian
Opt. Lett. 33(16) 1875-1877 (2008)

Indirect absorption spectroscopy using quantum cascade lasers: mid-infrared refractometry and photothermal spectroscopy

Marcel Pfeifer, Alexander Ruf, and Peer Fischer
Opt. Express 21(22) 25643-25654 (2013)

Fully reflective external-cavity setup for quantum-cascade lasers as a local oscillator in mid-infrared wavelength heterodyne spectroscopy

Dušan Stupar, Jürgen Krieg, Peter Krötz, Guido Sonnabend, Manuela Sornig, Thomas F. Giesen, and Rudolf Schieder
Appl. Opt. 47(16) 2993-2997 (2008)

Mid-infrared external-cavity quantum-cascade laser

G. Totschnig, F. Winter, V. Pustogov, J. Faist, and A. Müller
Opt. Lett. 27(20) 1788-1790 (2002)