A bolometric hyperspectral camera based on a birefringent interferometer for remote sensing in the thermal infrared

Remote sensing in the thermal infrared (TIR) band (3-14 μm) is an increasingly attractive tool for environmental sciences and security due to its chemical specificity and the large spectral superposition with the atmospheric transparency window. Currently, the technique is largely dominated by dispersive-type hyperspectral imagers, which usually require expensive, cumbersome and cooled quantum detectors setups to compensate for their low optical throughput. Here, we present a compact and low-cost hyperspectral camera based on the Fourier-transform approach. Its main element is a common-path birefringent interferometer made of TIR-transparent crystal calomel (Hg₂Cl₂). We characterize it with both coherent and incoherent sources in the TIR, determining high optical throughput, adjustable spectral resolution up to 4.5 cm⁻¹, interferometric contrast higher than 90% even for incoherent radiation and a robust and long-term interferometric stability. By coupling the interferometer to an uncooled microbolometer detector with 640x480 pixels, we demonstrate hyperspectral imaging in the 8-14 μm spectral range for transmission and emission remote measurements.