We introduce a slit array metamaterial perfect absorber (SAMPA)  consisting of a dielectric layer sandwiched between two Au layers of which the upper layer is perforated with a periodic array of slits. This structure combines the principle of Extraordinary Optical Transmission (more light is transmitted through a hole than is incident on its surface) with that of Perfect Absorption (reflectance and transmittance are virtually zero). Accordingly, within the slights the electric fields are strongly enhanced and light-matter interaction is correspondingly greatly amplified. Thus, already small concentrations of analytes down to a monolayer can be detected and identified by their spectral fingerprints with a standard mid-infrared spectrometer.
Closely related to the SAMPAs are plasmonic slit absorbers, which simply consist of slit arrays in thin gold layers deposited on a layer of Si3N4. These slit arrays operate like unstructured gold layers if the incident light is polarized parallel to the long slit axes. In contrast, for light polarized perpendicular to the long slit axis, the plasmon is excited. By the introduction of a second slit, which is rotated relative to the first slit, both principal polarization states excite plasmon resonances which can be made to differ in wavelength. As a consequence, the operating wavelength range of this slit array can be tuned by adjusting the polarization state of the incoming light.
 Mayerhöfer, T.G., et al.. ACS Photonics, 2015. 2(11): p. 1567-1575.
 Knipper, R., et. al., in preparation.