Balanced-detection interferometric cavity-assisted photothermal spectroscopy

• DOI: 10.1364/oe.27.012183
• Publication Date: 2019-04-17T22:30:56Z
• Authors: Johannes P. Waclawek; Christian Kristament; Harald Moser; Bernhard Lendl
• Keywords: Quantum cascade laser; Photothermal spectroscopy

An optical cavity can be utilized as an excellent transducer for highly sensitive gas detection with the application of photothermal spectroscopy, featuring beneficial property ultra-low absorption volume within a rugged sensing element. We report novel implementation balanced in Fabry-Perot interferometry via two identical 1 mm-spaced cavities. That way, excess noise limiting sensitivity previous cavity-based sensors was effectively rejected close to fundamental limit shot noise. A quantum cascade laser served mid-infrared excitation source induce refractive index changes sample, and near-infrared fiber probe monitor photo-induced variations. The metrological qualities sensor were investigated by SO2 detection. For targeted band centered at 1380.93 cm-1, 5 ppbv minimum achieved s integration time, corresponding normalized equivalent 7.5 × 10-9 cm-1 W Hz-1/2. Additionally, showed long-term stability, enabling times few thousand seconds.