Infrared surface-plasmon-resonance attenuator for broadly controllable effective radiant temperature

We describe a controllable infrared plasmonic laser attenuator with application to infrared detector characterization. The device promises a broad range of effective radiant temperature and fine temperature control/resolution near ambient. The enabling mechanism is controllably-frustrated surface-plasmon-resonance using a Kretschmann prism coupler. The predicted wide dynamic range depends on optical and geometric tolerances for the coupler. To investigate these, a mid-wave-infrared coupler comprising a conducting Ga-doped ZnO film deposited directly on a right-angle sapphire prism was fabricated, tested, and compared with theory. The attenuation resonance was observed by measuring specular reflection of a p-polarized quantum cascade laser beam at 4.45 mu m wavelength as a function of internal incidence angle from the coated prism face. The predicted resonance for comparison was based on ellipsometrically-obtained optical constants and film thickness. Near perfect match between theory and experiment was achieved after adjusting for experimental uncertainties in optical parameters. The results quantify the accuracy and precision with which optical constants and geometrical parameters must be known to achieve the predicted performance.