The Nulling Interferometry Cryogenic Experiment (NICE): Architecture, requirements, and preliminary warm precursor results

TL;DR

The paper introduces NICE, a cryogenic mid-infrared nulling interferometry testbed, designed to validate LIFE’s high-contrast beam combiner. It establishes stringent requirements for raw null depth, throughput, and stability, and details a warm bench precursor that achieves a mean null depth around $7\times10^{-6}$ at $4.7\mu$m with a single-output throughput of $22\%$, approaching the target broadband performance. The methodology combines a symmetric optical chain, metrology-driven control, and a comprehensive error budget to quantify static and dynamic perturbations, with a clear path toward broadband, polarization-agnostic operation and eventual cryogenic deployment. The work demonstrates a significant step toward LIFE technology readiness by bridging existing high-contrast nulling capabilities with the cryogenic, high-throughput demands of a space-based exoplanet survey instrument, while outlining the remaining subsystems and integration challenges for full mission readiness.

Abstract

The success of the Large Interferometer For Exoplanets (LIFE) space mission depends on measuring the faint mid-infrared emission spectra of exoplanets while suppressing the glare of a host star. This requires an instrument capable of high-contrast nulling interferometry with exceptional sensitivity. While previous testbeds have proven the principle of deep, stable nulls, they have not combined high contrast with the high throughput and cryogenic operation required for LIFE. Here, we present the architecture of the Nulling Interferometry Cryogenic Experiment (NICE), a mid-infrared nulling testbed, to increase the technological readiness of LIFE. We derive the laboratory requirements necessary to validate the LIFE beam combiner and present the optical design of NICE. Finally, we report results from the ambient \enquote{Warm Bench} precursor, which has successfully demonstrated the required null depth ($< 10^{-5}$) using a polarized narrowband 4.7 um source, and the required throughput (> 17%) using one of the two nulling channels.

Figures (9)

• Figure 1: A sample of the best measured raw null depths with on-sky nulling facilities and testbeds, compared with the requirement for NICE, derived in \ref{['sec:nice1-requirements']}. Rectangular markers denote nulls with more than 2% spectral bandwidth, and circles denote narrowband nulls.
• Figure 2: Left: Transmission of a Single-Bracewell nuller at 8 as a function of on-sky angle for an ideal instrument and a perturbed instrument with degraded visibility. The baseline is optimized for an Earth-twin around a Solar-type star (shaded region) at a distance of 10. The transmission at an on-sky angle of zero is called the on-axis null depth. Right: The SNR of the instrument degrades as the on-axis null depth worsens because of increased stellar leakage, shown here at 8 wavelength. We set a requirement of at most 10% reduction in SNR from instrument errors.
• Figure 3: Requirement on the null depth power spectrum at 8. Assuming one rotation of the array per day, NICE requires a stability of the null depth of 6.0e-7 RMS from 170330 (black line) for a Single-Bracewell interferometer to act as the beam combiner in LIFE. The expected spectral signature of a planet is also shown.
• Figure 4: Preliminary optical diagram of NICE. QPDs are quadrant photodiodes for the metrology, and PDs are regular photodiodes. The electrical signals $A_1$ and $A_2$ are amplitude-modulated drive signals for the acousto-optic modulators (AOMs)
• Figure 5: Optical diagram of the Warm Bench, a precursor for NICE at ambient conditions, as it was used for the measurements.