The next generation of mid-IR laser-based refractive index (dispersion) spectroscopy of liquid-phase analytes

Abstract

Mid-infrared dispersion spectroscopy is a novel alternative approach to classical absorption spectroscopy for qualitative and quantitative analysis of liquid-phase samples. We present a miniaturized external cavity-quantum cascade laser-based Mach-Zehnder interferometer setup for dispersion (refractive index) sensing of liquids (i.e., carbohydrates). The setup features high thermal and mechanical stability and reproducibility owing to extensive temperature and environmental control, setup miniaturization as well as the implementation of a new dual-channel transmission cell and a hysteresis-free piezo-actuator for phase locked interferometric detection. Due to the setup’s sensitivity to real and imaginary part of the refractive index, dispersion and absorption spectra can be acquired from a single sample and used for internal comparison and referencing.