Mid-infrared photodetection using a resonant nanocavity array of coupled surface plasmon-phonon polaritons*

Polar dielectric crystals are a promising ingredient in mid-far infrared photodetection because strong coupling of infrared light and surface polarized ion vibrations at Reststrahlen band provides a unique channel between photon and phonon via electric charge oscillations. In addition, there are many polar dielectrics in which the Reststrahlen band spreads widely from mid to far infrared spectral range where few photo-detection mechanisms are developed. Here, we report mid-infrared photodetection from the coupled surface plasmon-phonon polariton cavity resonance. The metal (gold)- insulator (Si) aperture array on polar dielectric (SiC) crystal forms a Farbry-Perot cavity and shows frequency-tunable high absorption up to 80% of the optical power at 10 – 12 micron wavelengths. The top metal is connected to an electrode outside the nanocavity array to get a photovoltaic signal. We utilized a tunable quantum cascade laser integrated into an infrared microscope and Fourier transform spectrometer. We ran voltage sensitive needles, in contact with the electrode pads, to a lock-in amplifier which could determine the incoming infrared signal when contrasted with the frequency of an optical chopper. We observe micro-volt photovoltaic signal with respect to the chopper frequency.