Ppb detection level's hydrogen sensor using a SPR grating in the triggered switching configuration

Abstract

An optical plasmonic hydrogen sensor is proposed, based on what we believe to be a novel configuration named plasmon-triggered switching. This configuration, involving two propagative orders diffracted by a deep metallic grating combined to a hydrogen-sensitive layer, is capable of measuring hydrogen concentrations. The two diffracted orders enable a differential measurement, which estimates a change of refractive index through evolution of the relative diffraction efficiency of each order at fixed wavelength and fixed angle, while cancelling any drift of the input laser source and other disturbances and allowing both a high sensitivity and a very low limit of detection (LOD). Experimental results, using a simple implementation involving one laser and two detectors, demonstrate a LOD without any signal post-processing, below 0.2 ppm (2.10^-5% Vol) in filtered air, are in good agreement with simulations and exhibit very good repeatability. The proposed setup represents a very promising, compact and cost-efficient approach to real-time hydrogen sensing using a thin H₂ sensitive and selective palladium thin layer deposited on a gold grating for highly sensitive plasmon coupling.