Dual-color superlattice thermal imager remotely senses carbon dioxide

Bispectral mid-IR imaging detectors have capabilities that single-color versions don’t, including absolute remote temperature measurement and a heightened ability to pick objects out from cluttered backgrounds based on spectral signatures. Researchers at the Fraunhofer-Institut für Angewandte Festkörperphysik (Freiburg, Germany) have developed a dual-color thermal superlattice focal-plane array (FPA) based on indium arsenide/gallium antimonide, which is less expensive than the mercury cadmium telluride used in prevalent devices. The device is especially well suited for remote imaging of carbon dioxide, which emits strongly at 4.2 µm.

The 288 × 384-pixel FPAs are lithographically fabricated in batches of four on full wafers. Each FPA is 16.1 × 12.1 mm in size and is flip-chip hybridized to a silicon readout integrated circuit, which supports snapshot integration and individual control of bias for both colors. The 50%-cutoff wavelengths for the two (“blue” and “red”) channels are 4.0 and 5.0 µm at 77 K. The FPA is cooled by a Sterling cooler. The blue and red channels a noise-equivalent temperature difference of 29 and 16.5 mK, respectively. The carbon dioxide signature is enhanced by subtracting the blue from the red signal. Contact Robert Rehm at[email protected].