Angular interrogation of evanescent wave absorption spectroscopy based sensors for harsh environment sensing applications

Evanescent wave absorption spectroscopy (EWAS) based sensors offer a number of unique advantages which include compatibility with remote optical sensing, simplicity of sensor design, low cost of sensing elements, and compatibility with harsh environment sensing applications. A number of different sensor-materials exist for the sensing of various chemical and environmental parameters and signal-to-noise ratios (SNRs) for such devices are dictated by a complex interplay of device design and sensing material selection for the EWAS configuration. In this work, we report that one effective way to optimize SNRs for a fixed sensor device / material design is through unique interrogation methods including angular selectivity in the sensor interrogator. We theoretically illustrate the origins of the signal optimization technique, and demonstrate feasibility using an EWAS sensor designed for harsh-environment pH sensing.