Physical mechanism of reflectance inversion in hydrogen gas sensor with Pd/PVDF structures

The physical mechanism of the reflectance inversion phenomena observed in thin-film Pd on polyvinylidene fluoride (PVDF) optical hydrogen sensor structures (Pd/PVDF) upon exposure to hydrogen gas has been investigated. Based on experimental observations using sensors with or without a metallic back-surface coating, a theoretical model taking into account the infinite optical interreflections within the transparent polymer PVDF has been proposed. The understanding of the origin of the reflectance inversion is helpful in optimizing the design and performance of optical hydrogen sensors with Pd-layer active element structures.