Robust Attenuated Total Reflection Infrared Spectroscopic Sensors Based on Quantum Cascade Lasers for Harsh Environments

A compact yet robust sensor system for applications in harsh environments has been developed. The sensor takes advantage of infrared attenuated total reflection (IR-ATR) spectroscopy with an invariant coupling of IR radiation into the ATR sensing element via substrate-integrated hollow waveguides (iHWGs). The system design, which is supported by appropriate simulations, minimizes the influence of environmental parameters (e.g., hydrostatic pressure, mechanical vibrations, etc.) at the optically delicate ATR waveguide. Next to an innovative radiation coupling concept via iHWGs in lieu of conventional optics, IR-transparent fibers were used. The fibers ensure a direct optical connection of the quantum cascade laser (QCL) light source and the detector to the iHWG coupling elements of the sensor cell.