QCL-based photothermal spectroscopy of liquids: from a bench-top Mach Zehnder interferometer to using photonic integrated circuits

Mid-infrared (mid-IR) photothermal spectroscopy (PTS) is a non-destructive analytical technique offering qualitative and quantitative insights into target analytes. Using coherent mid-IR lasers, PTS detects small temperature-induced refractive index changes in the sample, surpassing the limitations of conventional absorption methods. We present a PTS system based on a Mach-Zehnder interferometer (MZI) for liquid detection. In the context of liquid analysis using similar phase-sensitive apparatuses, an application of a benchtop digital-off-axis holography MZI will also be presented. In particular, the developed MZI setup enables imaging the changes in the ion-specific concentration of paramagnetic critical metal ions (e.g., Nd3+, Dy3+, Ni2+, and Co2+) during the ion enrichment process under applied magnetic fields. The magnetic field influences ion transport (magnetophoresis) by leveraging their magnetic susceptibility and the field gradient. Preliminary results demonstrate significant potential for designing efficient and selective systems for critical materials separation employing magnetic fields.