Hollow-Core-Fibre-Delivered Attenuated Total Internal Reflection Heterodyne Spectroscopy

Attenuated total internal reflection Fourier-transform infrared (ATR-FTIR) spectroscopy is a commonly used modality for measuring the spectra of highly absorbing liquids and solids. Previously, we combined broadband OPO-based mid-IR spectroscopy [1] with the use of a non-resonant hollow-core fibre (HCF) [2] to demonstrate heterodyne detection in a way that achieved common mode rejection of absorption features unique to the fibre transmission path [3]. We now extend this approach to enable simple, fibre-delivered ATR spectroscopy.