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The Large Interferometer For Exoplanets (LIFE) is an envisioned nulling interferometry space mission to characterize the atmospheres of terrestrial exoplanets in the mid-infrared (MIR) wavelength range (∼4-18.5 μm.) The star-to-planet flux contrast for an Earth-twin exoplanet is ≈ 107 at these wavelengths. Previous studies have shown that a “raw” null-depth of 105 provided by the interferometer is sufficient as long as the residual starlight can be removed through signal modulation, phase-chopping and data post processing. Two main technological challenges for a nulling interferometer are instrument stability and sensitivity. Several test-benches were built for LIFE’s ancestral mission concepts DARWIN and TPF-I. Operating at ambient conditions, they demonstrated excellent stability and suppressed the artificial starlight by up to 106 (depending on the spectral bandpass). However, instrument sensitivity/throughput for astronomical sources can not be characterized at background dominated ambient conditions. Cooling the instruments to cryogenic conditions reduces the thermal background and enables sensitivity driven instrument characterization. The Nulling Interferometer Cryogenic Experiment (NICE) is a single Bracewell nulling interferometer test-bench for LIFE. The ultimate aim of this test-bench is to attain a sensitivity level that demonstrates the feasibility of detecting an Earth-twin around a Sun-like star at 10 pc with a spectral bandwidth of 10% at 10 μm. The development of NICE is divided into two phases, the warm and cold phase. The warm phase focuses on the alignment of the optical components and maintaining their position and angular stability to achieve a null depth of 10−5 − 10−6 at 4 μm over several hours. In the cold phase, NICE will be cooled to 15 K to suppress the thermal background, and the throughput and sensitivity of the instrument will be characterized. This paper describes the development plan of NICE and presents the optical layout of the NICE warm phase. It also presents the preliminary null-depth reached by the NICE warm phase and the residual alignment errors in the system.
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