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

¹ Politecnico di Milano, Dipartimento di Fisica, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy
² Technische Universitӓt Wien, Wiedner Hauptstrasse 8-10/134, 1040 Wien, Austria
³ NIREOS S.R.L., Via G. Durando 39, 20158 Milano, Italy
⁴ IFN-CNR, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy
⁵ BBT-Materials Processing Ltd., Doubicka 11, 184 00 Prague 8, Czech Republic

^* Corresponding author: matteo1.corti@mail.polimi.it

Published online: 31 October 2024

Abstract

Remote sensing in thermal infrared bands (TIR) is largely dominated by cumbersome dispersive-type hyperspectral imagers, which usually require expensive and cryo-cooled quantum detectors to make up for their low optical throughput. Here, we present a compact and low-cost TIR hyperspectral camera based on the Fourier-transform approach. It combines an uncooled bolometer detector and a common-path birefringent interferometer made of calomel (Hg₂Cl₂). It features high optical throughput, an interferometric contrast greater than 90% even for incoherent radiation, spectral resolution tunable up to 4.5 cm^-1, robust and long-term interferometric stability. Retrieving in a few minutes the infrared spectrum in all pixels of the TIR image, it could constitute a valuable tool for evaluating radiative cooling materials’ spatial and spectral properties over extended areas. We test the capabilities of the instrument by measuring the emissivity map of different butterfly wings, which provide a natural example of radiative cooling.