Spectral Characterization of Mid-Infrared Bloch Surface Waves Excited on a Truncated 1D Photonic Crystal

The many fundamental roto-vibrational resonances of chemical compounds result in strong absorption lines in themid-infrared region (? ~ 2-20 ?m). For this reason, mid-infrared spectroscopy plays a key role in label-free sensing, in particular, forchemical recognition, but often lacks the required sensitivity to probe small numbers of molecules. In this work, we propose avibrational sensing scheme based on Bloch surface waves (BSWs) on 1D photonic crystals to increase the sensitivity of mid-infraredsensors. We report on the design and deposition of CaF2/ZnS 1D photonic crystals. Moreover, we theoretically and experimentallydemonstrate the possibility to sustain narrow ?-polarized BSW modes together with broader ?-polarized modes in the range of 3-8?m by means of a customized Fourier transform infrared spectroscopy setup. The multilayer stacks are deposited directly on CaF2prisms, reducing the number of unnecessary interfaces when exciting in the Kretschmann-Raether configuration. Finally, wecompare the performance of mid-IR sensors based on surface plasmon polaritons with the BSW-based sensor. The figures of meritfound for BSWs in terms of confinement of the electromagnetic field and propagation length puts them as forefrontrunners for labelfree and polarization-dependent sensing devices.