A thermal infrared hyperspectral camera based on a birefringent interferometer

We present a compact hyperspectral camera based on the Fourier-transform approach working in the thermal infrared (TIR) spectral region. The system is based on a common-path birefringent interferometer, made with the TIR transparent material calomel (Hg2Cl2), ensuring the generation of phase-locked light replicas and characterized by high delay accuracy, long-term stability and compactness. Compared to previous designs, the interferometer presented here greatly improves the spatial coherence of the replicas, enabling its applications also to the challenging TIR range. We demonstrate interferometric contrast higher than 90%, spectral resolution below 4.5 cm−1, and a spectral coverage between 3 and 14 μm, limited only by the detector and its optical components. By coupling the interferometer to an uncooled microbolometer with 640 × 480 pixels, we demonstrate hyperspectral imaging in the 8-14 μm range, remotely acquiring emission and transmission spectra from each point of a scene.