Toward Bloch Surface Wave-Assisted Spectroscopy in the Mid-Infrared Region

We present the first observation of Bloch surface waves in the mid-infrared spectral range. Bloch surface waves are electromagnetic states that can propagate at the interface between a continuous dielectric medium and a periodic stack of materials. We designed a mid-infrared multilayer optical element specifically for this purpose. The structure is made of successive layers of ZnSe and YbF3 deposited on a CaF2 substrate. Surface waves can be coupled into this structure from 6.6 to 10.6 μm. We characterized the optical properties of the fabricated element using a tunable quantum cascade laser centered around 7.85 μm. We believe that Bloch surface wave based platforms are very promising components for surface sensing and spectroscopic applications in the mid-infrared.