Qualification of infrared optical fibers and emitters for a spectrometer for <i>in situ</i> planetary exploration: Results from the TRIS (TRansmission and Illumination System) project

Visible-infrared spectroscopy has played a key role in in situ planetary exploration, enabling investigation of the composition and physical properties of rocky bodies. Extending these measurements into the mid-infrared (MIR) region provides access to diagnostic spectral bands directly linked to surface composition. However, this requires optical components capable of operating under harsh space conditions. This work presents the results of the TRansmission and Illumination System (TRIS) program, aimed at qualifying infrared optical fibers and emitters for planetary spectrometers. Indium fluoride (InF3) optical fibers were characterized over the 0.3-5.5 μm range, while micro-electromechanical systems infrared sources were analyzed between 1 and 20 μm using Fourier-transform infrared spectroscopy, confirming stable blackbody behavior. Both components were subjected to thermo-vacuum cycling (100-240 K) and gamma radiation up to a total ionizing dose of 375 Gy. Building on previous work on radiation effects in InF3 fibers, this study extends the analysis to combined environmental conditions and provides, to the best of our knowledge, the first joint experimental assessment of optical fibers and infrared emitters under conditions representative of planetary missions. The results show stable performance in the MIR range, with radiation-induced effects mainly confined to the visible region and not affecting the TRIS operational band. Thermo-mechanical stress was identified as the primary driver of structural degradation, leading to localized damage under constrained conditions. These findings support the use of InF3 fibers and IR emitters in next-generation in situ planetary spectrometers, while highlighting key mechanical design considerations for reliable operation in space environments.