Development of a wide‑band imaging FT‑IR using wavefront‑division interferometry for future planetary and space‑exploration payloads

Abstract

We developed a compact imaging Fourier transform infrared (FT-IR) spectrometer based on wavefront-division interferometry for planetary exploration and small-satellite missions. The instrument covers 4–20 μm with a wavenumber resolution of 3.8 cm−1 and a spatial resolution of 34 μm. The optical system uses two Zernike freeform mirrors and a pair of plane mirrors, while an uncooled mid-infrared camera records an interferogram at each pixel (640×480, 17 μm), enabling two-dimensional spectroscopy in a single scan. Because the optical path difference is generated in a common-path configuration, the system is compact and tolerant to vibration. To improve spatial coherence under extended-source illumination, we introduced a Wavefront Pre-Selection Mask (WPSM) at the entrance plane. The WPSM increases the center-burst amplitude by approximately 50 times and improves fringe visibility by about a factor of two. Wavenumber accuracy was evaluated using a 960 cm−1 quantum cascade laser, yielding a mean offset of 0.05 cm−1. Measurements of a JASCO polystyrene standard film also showed good agreement with reference spectra. These results demonstrate that the proposed wavefront-division FT-IR architecture provides accurate two-dimensional infrared spectroscopy in a compact and vibration-tolerant instrument suitable for planetary and small-satellite missions.